# Ncert Class 6 Mathematics Solutions Chapter 3

## Ncert Class 6 Mathematics Solutions Chapter 3 Playing with Numbers

Welcome to NCTB Solutions. Here with this post we are going to help 6th class students for the Solutions of NCERT Class 6 Mathematics Book, Chapter 3, Playing with Numbers. Here students can easily find step by step solutions of all the problems for Playing with Numbers, Exercise 3.1, 3.2, 3.3, 3.4, 3.5, 3.6 and 3.7 Also here our mathematics teacher’s are solved all the problems with easily understandable methods with proper guidance so that all the students can understand easily. Here in this post students will get chapter 3 solutions. Here all the solutions are based on NCERT latest syllabus.

Playing with Numbers Exercise 3.1 Solution :

(1) Write all the factors of the following numbers :

(a) 24 (b) 15

(c) 21 (d) 27

(e) 12 (f) 20

(g) 18 (h) 23

(i) 36

Solution :

(a) 24

The factors of 24

24 = 1 × 24, 2 × 12, 3 × 8, 4 × 6

The factors of 24 is 1, 2, 3, 4, 6, 12, 24

(b) 15

The factors of 15

15 = 1 × 15, 3 × 5

The factors of 15 is 1, 3, 5, 15

(c) 21

The factors of 21

21 = 1 × 21, 3 × 7

The factors of 21 is 1, 3, 7, 21

(d) 27

The factors of 21

27 = 1 × 27, 3 × 9

The factors of 21 is 1, 3, 9, 27

(e) 12

The factors of 12

12 = 1 × 12, 2 × 6, 3 × 4

The factors of 12 is 1, 2, 3, 4, 6, 12

(f) 20

The factors of 20

20 = 1 × 20, 2 × 10, 4 × 5

The factors of 24 is 1, 2, 4, 5, 10, 20

(g) 18

The factors of 18

18 = 1 × 18, 2 × 9, 3 × 6

The factors of 12 is 1, 2, 3, 6, 9, 18

(h) 23

The factors of 23

23 = 1 × 23

The factors of 23 is 1, 23

(i) 36

The factors of 36

36 = 1 × 36, 2 × 18, 3 × 12, 4 × 9, 6 × 6

The factors of 24 is 1, 2, 3, 4, 6, 9, 12, 36

(2) Write first five multiples of (a) 5 (b) 8 (c) 9

Solution :

(a) 5

First five multiples of 5 = 5 × 1, 5 × 2, 5 × 3, 5 × 4, 5 × 5

First five multiples of 5 is 5, 10, 15, 20, 25

(b) 8

First five multiples of 8 = 8 × 1, 8 × 2, 8 × 3, 8 × 4, 8 × 5

First five multiples of 8 is 8, 16, 24, 32, 40

(c) 9

First five multiples of 9 = 9 × 1, 9 × 2, 9 × 3, 9 × 4, 9 × 5

First five multiples of 9 is 9, 18, 27, 36, 45

(4) Find all the multiples of 9 upto 100.

Solution :

The multiples of 9 up to 100

Multiples of 9 = 9 × 1, 9 × 2, 9×3, 9× 4, 9×5, 9×6, 9 ×7, 9 × 8, 9 × 9, 9 × 10, 9 ×11.

Multiples of 9 = 9, 18, 27, 36, 45, 54, 63, 72, 81, 90, 99

Playing with Numbers Exercise 3.2 Solution :

(1) What is the sum of any two (a) Odd numbers? (b) Even numbers?

Solution :

(a) Odd numbers?

= Sum of any two Odd numbers is even number.

(b) Even numbers?

= Sum of any two Even numbers is even number.

(2) State whether the following statements are True or False:

(a) The sum of three odd numbers is even.

(b) The sum of two odd numbers and one even number is even.

(c) The product of three odd numbers is odd.

(d) If an even number is divided by 2, the quotient is always odd.

(e) All prime numbers are odd.

(f) Prime numbers do not have any factors.

(g) Sum of two prime numbers is always even.

(h) 2 is the only even prime number.

(i) All even numbers are composite numbers.

(j) The product of two even numbers is always even.

Solution :

(a) False.

Reason : the sum of three odd numbers is odd.

(b) True.

(c) True.

(d) False

Reason :  If an even number is divided by 2, the quotient is always even.

(e) False

Reason : Except 2 all prime numbers are odd.

(f) False

Reason : Prime numbers have factors.

(g) False.

Reason : Sum of two prime numbers is always odd.

(h) True

(i) False.

Reason : All even numbers are not composite numbers.

(j) True

Explanation : Let, Two even numbers, = 10, 12

= 12 × 10

= 120 (Even)

Again, two ever numbers = 2, 4

= 2 × 4

= 8 (Ever)

So, Yes product of two even number always a even number.

(3) The numbers 13 and 31 are prime numbers. Both these numbers have same digits 1 and 3. Find such pairs of prime numbers upto 100.

Solution :

17 and 71, 37 and 73, 79 and 97 are the pairs of prime numbers.

(4) Write down separately the prime and composite numbers less than 20.

Solution :

Primer number mean the number which is divided by only 1 and itself whereas Composite number is the number which is divided by other number except 1 and itself.

Prime numbers less than 20: 2, 3, 5, 7, 11, 13, 17, 19

Composite numbers less than 20: 4, 6, 8, 9, 10, 12, 14, 15, 16, 18

(5) What is the greatest prime number between 1 and 10?

Solution :

Prime number between 1 and 10 are following 2, 3, 5, 7

So, 7 is the greatest prime number between 1 and 10

(6) Express the following as the sum of two odd primes.

(a) 44 (b) 36 (c) 24 (d) 18

Solution :

(a) 44

= 3 + 41 (13 + 31)

(b) 36

= 5 + 31 (17 + 19)

(c) 24

= 5 + 19 (11 + 13)

(d) 18

= 5 + 13 (7 + 11)

(7) Give three pairs of prime numbers whose difference is 2.

Solution :

3, 5; 5, 7 ; 11, 13 ; 41,43 are three pairs of prime numbers whose difference is 2.

(8) Which of the following numbers are prime?

(a) 23 (b) 51 (c) 37 (d) 26

Solution :

(a) 23, (c) 37 are prime numbers.

(9) Write seven consecutive composite numbers less than 100 so that there is no prime number between them.

Solution :

The numbers are – 90, 91, 92, 93, 95, 96

(10) Express each of the following numbers as the sum of three odd primes:

(a) 21 (b) 31 (c) 53 (d) 61

Solution :

(a) 21

= 3 + 5 + 13

(b) 31

= 3 + 5 + 23 or 11+ 13 +7

(c) 53

= 11 + 13 + 29

(d) 61

= 7 + 13 + 41

(11) Write five pairs of prime numbers less than 20 whose sum is divisible by 5.

Solution :

2 + 3 = 5;

2 + 13 = 15;

3 + 17 = 20;

7 + 13 = 20;

11 + 19 = 20

All these sum is divisible by 5.

Hence, Five pairs of prime numbers less than 20 are 2, 3; 2, 13; 3, 17; 7, 13; 11, 19

(12) Fill in the blanks :

(a) A number which has only two factors is called a ___.

(b) A number which has more than two factors is called a ___.

(c) 1 is neither ___ nor ___.

(d) The smallest prime number is ___.

(e) The smallest composite number is ___.

(f) The smallest even number is ___.

Solution :

(a) prime number.

(b) composite number.

(c) prime, composite

(d) -2

(e) 4

(f) 2

Playing with Numbers Exercise 3.3 Solution :

(2) Using divisibility tests, determine which of the following numbers are divisible by 4; by 8 :

(a) 572 (b) 726352 (c) 5500 (d) 6000

(e) 12159 (f) 14560 (g) 21084

(h) 31795072 (i) 1700 (j) 2150

Solution :

(a) 572

divisibility tests of 4 =number contain last two digit 0 or last two number are divisible by 4 then the number is divisible by 4.

Divisibility tests of 8 =number contain last Three digit 0 or last three number are divisible by 8 then the number is divisible by 8.

72 is the last number which is divisible by 4

572 is divisible by 4.

(b) 726352

Divisibility tests of 4 =number contain last two digit 0 or last two number are divisible by 4 then the number is divisible by 4.

Divisibility tests of 8 =number contain last Three digit 0 or last three number are divisible by 8 then the number is divisible by 8.

52 is the last number which is divisible by 4

352 is the last number which is divisible by 8.

726352 is divisible by 4 and 8

(c) 5500

Divisibility tests of 4 =number contain last two digit 0 or last two number are divisible by 4 then the number is divisible by 4.

Divisibility tests of 8 number contain last Three digit 0 or last three number are divisible by 8 then the number is divisible by 8.

00 is the last number which is divisible by 4

5500 is divisible by 4

(d) 6000

Divisibility tests of 4 =number contain last two digit 0 or last two number are divisible by 4 then the number is divisible by 4.

Divisibility tests of 8 =number contain last Three digit 0 or last three number are divisible by 8 then the number is divisible by 8.

00 is the last number which is divisible by 4

000 the last number which is divisible by 8

6000 is divisible by 4 and 8

(e) 12159

= 12159 is not divisible by 4 or 8

(f) 14560

Divisibility tests of 4 =number contain last two digit 0 or last two number are divisible by 4 then the number is divisible by 4.

Divisibility tests of 8 =number contain last Three digit 0 or last three number are divisible by 8 then the number is divisible by 8.

60 is the last number which is divisible by 4

560 is the last number which is divisible by 8.

14560 is divisible by 4 and 8

(g) 21084

Divisibility tests of 4 =number contain last two digit 0 or last two number are divisible by 4 then the number is divisible by 4.

Divisibility tests of 8 =number contain last Three digit 0 or last three number are divisible by 8 then the number is divisible by 8.

84 is the last number which is divisible by 4

21084 is divisible by 4

(h) 31795072

Divisibility tests of 4 =number contain last two digit 0 or last two number are divisible by 4 then the number is divisible by 4.

Divisibility tests of 8 =number contain last Three digit 0 or last three number are divisible by 8 then the number is divisible by 8.

72 is the last number which is divisible by 4

072 is the last number which is divisible by 8

31795072 is divisible by 4 and 8

(i) 1700

Divisibility tests of 4 =number contain last two digit 0 or last two number are divisible by 4 then the number is divisible by 4.

Divisibility tests of 8 =number contain last Three digit 0 or last three number are divisible by 8 then the number is divisible by 8.

00 is the last number which is divisible by 4

1700 is divisible by 4

(j) 2150

2150 is not divisible by 4 or 8

(3) Using divisibility tests, determine which of following numbers are divisible by 6:

(a) 297144 (b) 1258 (c) 4335 (d) 61233 (e) 901352

(f) 438750 (g) 1790184 (h) 12583 (i) 639210 (j) 17852

Solution :

(a) 297144

Divisibility test 6 = the numbers which are even and divisible by 3 are divisible by 6.

297144 = this is even number and divisible by 3.

297144 is divisible by 6

(b) 1258

Divisibility test 6 = the numbers which are even and divisible by 3 are divisible by 6.

1258 = this is even number but not divisible by 3.

1258 is not divisible by 6

(c) 4335

Divisibility test 6 = the numbers which are even and divisible by 3 are divisible by 6.

4335 = this is not even number.

4335 is not divisible by 6

(d) 61233

Divisibility test 6 = the numbers which are even and divisible by 3 are divisible by 6.

61233 = this is not even number

61233 is not divisible by 6

(e) 901352

Divisibility test 6 = the numbers which are even and divisible by 3 are divisible by 6.

901352 = this is even number but not divisible by 3.

901352 is not divisible by 6

(f) 438750

Divisibility test 6 = the numbers which are even and divisible by 3 are divisible by 6.

438750 = this is even number and divisible by 3.

438750 is divisible by 6

(g) 1790184

Divisibility test 6 = the numbers which are even and divisible by 3 are divisible by 6.

1790184= this is even number and divisible by 3.

1790184 is divisible by 6

(h) 12583

Divisibility test 6 = the numbers which are even and divisible by 3 are divisible by 6.

12583 = this is not even number

12583 is not divisible by 6

(i) 639210

Divisibility test 6 = the numbers which are even and divisible by 3 are divisible by 6.

639210 = this is even number and divisible by 3.

639210 is divisible by 6

(j) 17852

Divisibility test 6 = the numbers which are even and divisible by 3 are divisible by 6.

17852= this is even number but not divisible by 3.

17852 is not divisible by 6

(4) Using divisibility tests, determine which of the following numbers are divisible by 11 :

(a) 5445 (b) 10824

(c) 7138965 (d) 70169308

(e) 10000001 (f) 901153

Solution :

(a) 5445

Divisibility test of 11 = we are adding alternate number and subtract the sum which we get and this result are 0 or multiple of 11 then the number is divisible by 11.

By adding alternate numbers 5 + 4 = 9 and 4 + 5 = 9

Subtracting sum = 9 -9 = 0

5445 is divisible by 11.

(b) 10824

Divisibility test of 11 = we are adding alternate number and subtract the sum which we get and this result are 0 or multiple of 11 then the number is divisible by 11.

By adding alternate numbers 4 + 8 +1 = 13 and 2 + 0 = 2

Subtracting sum = 13 -2 = 11

10824 is divisible by 11.

(c) 7138965

Divisibility test of 11 = we are adding alternate number and subtract the sum which we get and this result are 0 or multiple of 11 then the number is divisible by 11.

By adding alternate numbers 5 + 9 +3 +7 = 24 and 6 + 8 + 1 = 15

Subtracting sum = 24 -15 = 9

7138965 is not divisible by 11.

(d) 70169308

Divisibility test of 11 = we are adding alternate number and subtract the sum which we get and this result are 0 or multiple of 11 then the number is divisible by 11.

By adding alternate numbers 8 + 3 +6 +0 = 17 and 0 + 9 + 1 + 7 = 17

Subtracting sum = 17 -17 = 0

70169308 is divisible by 11.

(e) 10000001

Divisibility test of 11 = we are adding alternate number and subtract the sum which we get and this result are 0 or multiple of 11 then the number is divisible by 11.

By adding alternate numbers 1+ 0 +0+0 = 1 and 0 + 0 + 0 + 1 = 1

Subtracting sum = 1 -1 = 0

10000001 is divisible by 11.

(f) 901153

Divisibility test of 11 = we are adding alternate number and subtract the sum which we get and this result are 0 or multiple of 11 then the number is divisible by 11.

By adding alternate numbers 3+ 1 +0 = 4 and 5 + 1 + 9 = 15

Subtracting sum = 15 -4 = 11

901153 is divisible by 11.

(5) Write the smallest digit and the greatest digit in the blank space of each of the following numbers so that the number formed is divisible by 3 :

(a) __ 6724

(b) 4765 __ 2

Solution :

(a) __ 6724

Divisible by 3 = adding all numbers and sum is divisible by 3 then the number is divisible by 3.

Smallest digit = 2 + 6 + 7 + 2 + 4 = 21 is divisible by 3.

Greatest digit = 8 + 6 + 7 + 2 + 4 = 27 is divisible by 3

Smallest digit = 2

Greatest digit = 8

(b) 4765 __ 2

Divisible by 3 = adding all numbers and sum is divisible by 3 then the number is divisible by 3.

Smallest digit = 4 + 7 + 6 + 5 + 0 + 2 = 24 is divisible by 3.

Greatest digit = 4 + 7 + 6 + 5 + 9 + 2 = 33 is divisible by 3

Smallest digit = 0

Greatest digit = 9

(6) Write a digit in the blank space of each of the following numbers so that the number formed is divisible by 11

(a) 92 __ 389

(b) 8 __ 9484

Solution :

(a) 92 __ 389

Divisibility test of 11 = we are adding alternate number and subtract the sum which we get and this result are 0 or multiple of 11 then the number is divisible by 11.

By adding alternate numbers 9 + 3 + 2 = 14 and 8 + ? + 9 =

Subtraction is must be zero or multiple of 11.

We put 8 on blank space.

9 + 3 + 2 = 14 and 8 + 8 + 9 =25

25 – 14 = 11

928389

(b) 8 __ 9484

Divisibility test of 11 = we are adding alternate number and subtract the sum which we get and this result are 0 or multiple of 11 then the number is divisible by 11.

By adding alternate numbers 4 + 4 + ? = and 8 + 9 + 8 = 25

Subtraction is must be zero or multiple of 11.

We put 6 on blank space.

4 + 4 + 6 = 14 and 8 + 9 + 8 = 25

25 – 14 = 11

8 6 9484

Playing with Numbers Exercise 3.4 Solution :

Find the common factors of :

(i) 15 and 25

(ii) 35 and 50

(iii) 20 and 28

Solution :

(i) 15 and 25

15 = 1 × 15 = 3 × 5;

25 = 1 × 25

= 5 × 5

∴ Factors of 15 are = 1, 3, 5, 15

∴ Factors of 25 are = 1, 5, 25

∴ Common factors are 1, 8, 5

(ii) 35 and 50

35 = 1 × 35 = 5 × 7

50 = 1 × 50 = 2 × 25 = 5 × 10

∴ Common factors are 1 and 5

(iii) 20 and 28

20 = 1 × 20 = 2 × 10 = 4 × 5

28 = 1 × 28 = 2 × 14 = 4 × 7

Common factors are 1, 2, 4

(2) Find the common factors of :

(a) 4, 8 and 12

(b) 5, 15 and 25

Solution :

(a) 4, 8 and 12

Factors of 4 = 1, 2, 4

Factors of 8 = 1, 2, 4, 8

Factors of 12 = 1, 2, 3, 4, 6

Common factors of 4, 8 and 12 are 1, 2, 4

(b) 5, 15 and 25

Factors of 5 = 1, 5

Factors of 15 = 1, 3, 5

Factors of 25 = 1, 5

Common factors of 5, 15 and 25 are 1,5.

(3) Find first three common multiples of :

(a) 6 and 8

(b) 12 and 18

Solution :

(a) 6 and 8

Multiples of 6 = 6, 12, 18, 24, 30, 36, 42, 48, 54, 60, 66, 72

Multiples of 8 = 8, 16, 24, 32, 40, 48, 56, 64, 72

First three common multiples of 6 and 8 are 24, 48, and 72

(b) 12 and 18

Multiples of 12 = 12, 24, 36, 48, 60, 72, 84, 96, 18, 120

Multiples of 18 = 18, 36, 54, 72, 90, 108, 126, 144

First three common multiples of 12 and 18 are 36, 72, and 108

(4) Write all the numbers less than 100 which are common multiples of 3 and 4.

Solution :

All the numbers less than 100 which are common multiples of 3 and 4 are 12, 24, 36, 48, 60, 72, 84, 96.

(5) Which of the following numbers are co-prime?

(a) 18 and 35; (b) 15 and 37

(c) 30 and 415; (d) 17 and 68

(e) 216 and 215; (f) 81 and 16

Solution :

(a) 18 and 35

Co-prime numbers are the numbers having only 1 as a common factor.

In 18 and 35 only 1 as a common factor.

18 and 35 are Co-prime numbers.

(b) 15 and 37

Co-prime numbers are the numbers having only 1 as a common factor.

In 15 and 37 only 1 as a common factor.

15 and 37 are Co-prime numbers.

(c) 30 and 415

Co-prime numbers are the numbers having only 1 as a common factor.

In 30 and 415 not a 1 as a common factor.

i.e. 30 and 415 also divisible by 5

30 and 415 are not Co-prime numbers.

(d) 17 and 68

Co-prime numbers are the numbers having only 1 as a common factor.

In 17 and 68 not a 1 as a common factor.

i.e. 17 and 68 also divisible by 17

17 and 68 are not Co-prime numbers.

(e) 216 and 215

Co-prime numbers are the numbers having only 1 as a common factor.

In 216 and 215 only 1 as a common factor.

216 and 215 are Co-prime numbers.

(f) 81 and 16

Co-prime numbers are the numbers having only 1 as a common factor.

In 81 and 16 only 1 as a common factor.

81 and 16 are Co-prime numbers.

(6) A number is divisible by both 5 and 12. By which other number will that number be always divisible?

Solution :

If a number is divisible by 5 and 12, then it will be divisible by 2, 3, 4, 6, 10, 15, 20, 30, 60.

(7) A number is divisible by 12. By what other numbers will that number be divisible?

Solution :

Factors of 12 = 1, 2, 3, 4, 6

A number is divisible by 12 is also divisible by 1, 2, 3, 4, 6.

Playing with Numbers Exercise 3.5 Solution :

(1) Here are two different factor trees for 60. Write the missing numbers.

Solution :

Missing numbers for Tree (i) are

Missing numbers for Tree (ii) are

(2) Which factors are not included in the prime factorisation of a composite number?

Solution :

1 and the number itself are not included in the prime factorisation of a composite number.

(3) Write the greatest 4-digit number and express it in terms of its prime factors.

Solution :

As we all know that,

Greatest 4-digit number is = 9999

9999 = 3 × 3 × 11 × 101

(4) Write the smallest 5-digit number and express it in the form of its prime factors.

Solution :

As we know that,

Smallest 5-digit number is = 10000

10000 = 2 × 2 × 2 × 2 × 5 × 5 × 5 × 5

(5) Find all the prime factors of 1729 and arrange them in ascending order. Now state the relation, if any; between two consecutive prime factors.

Solution :

All the prime factors of 1729

1729 = 7 × 13 × 19

The difference of two consecutive prime factors is 6.

(6) The product of three consecutive numbers is always divisible by 6. Verify this statement with the help of some examples

Solution :

The product of three consecutive numbers is always divisible by 6.

The three consecutive numbers are 2, 3 , 4

Product of three consecutive numbers,

= 2 × 3 × 4 = 24

24 is divisible by 6.

The product of three consecutive numbers is always divisible by 6. Verifies the statement.

(7) The sum of two consecutive odd numbers is divisible by 4. Verify this statement with the help of some examples.

Solution :

Two consecutive odd numbers = 3, 5

Sum of two consecutive odd numbers

= 3 + 5 = 8

8 is divisible by 4.

The sum of two consecutive odd numbers is divisible by 4. Verifies the statement.

(8) In which of the following expressions, prime factorisation has been done?

(a) 24 = 2 × 3 × 4

(b) 56 = 7 × 2 × 2 × 2

(c) 70 = 2 × 5 × 7

(d) 54 = 2 × 3 × 9

Solution :

In (b) 56 = 7 × 2 × 2 × 2

And (c) 70 = 2 × 5 × 7 prime factorisation has done.

(9) 18 is divisible by both 2 and 3. It is also divisible by 2 × 3 = 6. Similarly, a number is divisible by both 4 and 6. Can we say that the number must also be divisible by 4 × 6 = 24? If not, give an example to justify your answer.

Solution :

No,

This is Because Number 12 is divisible by both 4 and 6; but 12 is not divisible by 24.

(10) I am t210he smallest number, having four different prime factors. Can you find me?

Solution :

The smallest prime number is 2. Next is 3, 5, and 7.

Four consecutive prime numbers are 2, 3, 5, 7

Four different prime factors

= 2 × 3 × 5 × 7

= 210

Therefore, the smallest number is 210

Playing with Numbers Exercise 3.6 Solution :

(1) Find the HCF of the following numbers :

(a) 18, 48 (b) 30, 42

(c) 18, 60 (d) 27, 63

(e) 36, 84 (f) 34, 102

(g) 70, 105, 175 (h) 91, 112, 49

(i) 18, 54, 81 (j) 12, 45, 75

Solution :

(a) 18, 48

The Highest Common Factor (HCF) of two or more given numbers is the highest (or greatest) of their common factors.

Factors of 18 = 1,2,3,6,9,18

Factors of 48 =1, 2, 3,4,6,8,12,24,48

HCF of 18, 48 is 6

(b) 30, 42

Factors of 30 = 1, 2,3,5,6,10,15,30

Factors of 42 =1, 2, 3, 6,14,21,42

HCF of 30, 42 is 6

(c) 18, 60

Factors of 18 = 1, 2, 3, 6,9,18

Factors of 60 =1, 2, 3,4,5, 6,10,15,30,60

HCF of 18, 60 is 6

(d) 27, 63

Factors of 27 = 1, 3, 9, 27

Factors of 63 =1, 2, 3, 7, 9,

HCF of 27, 63 is 9

(e) 36, 84

Factors of 36 = 1, 2, 3, 9, 12, 36

Factors of 84 =1, 2, 3, 4, 6, 12, 42

HCF of 36, 84 is 12

(f) 34, 102

Factors of 34 = 1, 2, 17

Factors of 102 =1, 2, 3, 6, 17

HCF of 34, 102 is 17

(g) 70, 105, 175

Factors of 70 = 1, 2, 5,7, 10,35,70

Factors of 105 =1, 3, 5, 35,105

Factors of 175 =1,5,35

HCF of 70, 105, and 175 is 35

(h) 91, 112, 49

Factors of 91 = 1, 7, 13

Factors of 112 =1, 7, 14

Factors of 49 =1,7

HCF of 91, 112, and 49 is 7

(i) 18, 54, 81

Factors of 18 = 1, 2, 9.

Factors of 54 =1, 2, 3, 6, 9.

Factors of 81 =1, 3,9.

HCF of 18, 54, and 81 is 9

(j) 12, 45, 75

Factors of 12 = 1, 2, 3,4,6,12

Factors of 45 =1, 3, 5, 9, 45

Factors of 75 =1, 5,15,25.

HCF of 12, 45 and 75 is 1

(2) What is the HCF of two consecutive

(a) numbers?

(b) even numbers?

(c) odd numbers?

Solution :

(a) Example of two consecutive numbers = 5, 6

HCF of 5 and 6 = 1

HCF of two consecutive numbers is always 1.

(b) Two consecutive even numbers = 6, 8

HCF of 6, 8

= 2 ÷ 6 = 3

= 2 ÷ 8 = 4

HCF = 2

(c) Two consecutive odd numbers = 5, 7

HCF of 5, 7

= 5 ÷ 1 = 5

= 7 ÷ 1 = 7

HCF of 5, 7 is = 1

(3) HCF of co-prime numbers 4 and 15 was found as follows by factorisation : 4 = 2 × 2 and 15 = 3 × 5 since there is no common prime factor, so HCF of 4 and 15 is 0. Is the answer correct? If not, what is the correct HCF?

Solution :

4 = 2 × 2 and 15 = 3 × 5

Since there is no common prime factor, so HCF of 4 and 15 is 0.

This is wrong.

The correct HCF co-prime numbers 4 and 15 is 1 because only 1 is the common factor between them.

Playing with Numbers Exercise 3.7 Solution :

(1) Renu purchases two bags of fertiliser of weights 75 kg and 69 kg. Find the maximum value of weight which can measure the weight of the fertiliser exact number of times

Solution :

Renu purchases two bags of fertiliser of weights 75 kg and 69 kg.

Maximum value of weight which can measure the weight of the fertiliser exact number of times,

We have to find HCF of 75 kg and 69 kg

Factor of 75 = 1, 3, 5, 15, 25, 75

Factor of 69 = 1, 3,13, 23, 69

HCF of 75 kg and 69 kg is 3

The maximum value of weight is 3 kg.

(2) Three boys step off together from the same spot. Their steps measure 63 cm, 70 cm and 77 cm respectively. What is the minimum distance each should cover so that all can cover the distance in complete steps?

Solution :

Three boys step off together from the same spot

Their steps measure 63 cm, 70 cm and 77 cm respectively.

The minimum distance each should cover so that all can cover the distance in complete steps,

We have to find LCM of 63 cm, 70 cm and 77 cm respectively.

Factor of 63 = 1, 3, 7, 9, 21, 63

Factor of 70 =1, 2, 5,10,35,70

Factor of 77 =1, 7,11,77

LCM of 63 cm, 70 cm and 77 cm is 6930 cm.

The minimum distance each should cover so that all can cover the distance in complete steps is 6930 cm.

(3) The length, breadth and height of a room are 825 cm, 675 cm and 450 cm respectively. Find the longest tape which can measure the three dimensions of the room exactly.

Solution :

The length, breadth and height of a room are 825 cm, 675 cm and 450 cm respectively.

The longest tape which can measure the three dimensions of the room exactly,

We have to find HCF of 825 cm, 675 cm and 450 cm.

Factor of 825 = 1, 75

Factor of 675 = 1, 75

Factor of 450 = 1, 75

HCF of 825 cm, 675 cm and 450 cm is 75

The longest tape is 75 cm.

(4) Determine the smallest 3-digit number which is exactly divisible by 6, 8 and 12.

Solution :

The smallest 3-digit number which is exactly divisible by 6, 8 and 12.

We have to find LCM of 6, 8 and 12.

Factor of 6 = 1, 2, 3, 6

Factor of 8 = 1, 2, 4, 8

Factor of 12 = 1, 2, 3, 4, 6, 12

LCM of 6, 8 and 12 is 120

(5) Determine the greatest 3-digit number exactly divisible by 8, 10 and 12.

Solution :

The greatest 3-digit number exactly divisible by 8, 10 and 12.

We have to find LCM of 8, 10 and 12.

Factor of 8 =1, 2, 4, 8

Factor of 10 =1, 2, 5, 10

Factor of 12 =1, 2, 3, 4, 6, 12

LCM of 8, 10 and 12 is 960

(6) The traffic lights at three different road crossings change after every 48 seconds, 72 seconds and 108 seconds respectively. If they change simultaneously at 7 a.m., at what time will they change simultaneously again?

Solution :

The traffic lights at three different road crossings change after every 48 seconds, 72 seconds and 108 seconds respectively.

They change simultaneously at 7 a.m.

Time will they change simultaneously again = we have to find LCM of 48 seconds, 72 seconds and 108 seconds.

Factor of 48 =1, 2, 3, 4, 6, 8, 12,16,24,48

Factor of 72 =1, 2,3,4,6,8,9,12,18,24,36,72

Factor of 108 =1, 2, 3, 4,6,12,18,36,54,108

LCM of 48 seconds, 72 seconds and 108 seconds is 432 seconds.

432 seconds = 7 minutes 12 second.

Time will they change simultaneously again is 7 minutes 12 seconds past 7 a.m.

(7) Three tankers contain 403 litres, 434 litres and 465 litres of diesel respectively. Find the maximum capacity of a container that can measure the diesel of the three containers exact number of times.

Solution :

Three tankers contain 403 litres, 434 litres and 465 litres of diesel respectively.

Find the maximum capacity of a container that can measure the diesel of the three containers exact number of times.

We have to find HCF of 403 litres, 434 litres and 465 litres.

Factor of 403 = 1, 31

Factor of 434 = 1, 31

Factor of 465 = 1, 31

HCF of 403 litres, 434 litres and 465 litres is 31 litres.

Maximum capacity of a container is 31 litres.

(8) Find the least number which when divided by 6, 15 and 18 leave remainder 5 in each case.

Solution :

The least number which when divided by 6, 15 and 18 leave remainder 5 in each case.

We have to find LCM of 6, 15 and 18 and adding remainder 5

Factor of 6 = 1 × 2 × 3

Factor of 15 = 1 × 3 × 5

Factor of 18 = 1 × 3 × 6

LCM of 6, 15 and 18 is 90.

= 90 + 5

= 95

The least number which when divided by 6, 15 and 18 leave remainder 5 in each case is 95.

(9) Find the smallest 4-digit number which is divisible by 18, 24 and 32.

Solution :

The smallest 4-digit number which is divisible by 18, 24 and 32

We have to find LCM of 18, 24 and 32

Factor of 18 = 1 × 2 × 3 × 3

Factor of 24 = 1 × 2 × 3 × 4

Factor of 32 = 1 × 2 × 4 × 4

LCM of 18, 24 and 32 is 1152

(11) Find the LCM of the following numbers in which one number is the factor of the other.

(a) 5, 20

(b) 6, 18

(c) 12, 48

(d) 9, 45

What do you observe in the results obtained?

Solution :

(a) 5, 20

LCM of 5, 20

Factor of 5 = 1 × 5

Factor of 20 = 1 × 5 × 4

LCM of 5, 20 = 20

(b) 6, 18

LCM of 6, 18

Factor of 6 = 1 × 6

Factor of 18 = 1 × 6 × 3

LCM of 6, 18 = 18

(c) 12, 48

LCM of 12, 48

Factor of 12 = 1 × 12

Factor of 48 = 1 × 12 × 4

LCM of 12, 48 = 48

(d) 9, 45

LCM of 9, 45

Factor of 9 = 1 × 9

Factor of 45 = 1 × 9 × 5

LCM of 9, 45 = 45

LCM is the highest number.

Next Chapter Solution :

Updated: June 26, 2023 — 9:21 am