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**Brilliant’s Composite Mathematics Class 8 Solutions Chapter 18 Statistics**

Welcome to NCTB Solutions. Here with this post we are going to help 8th class students for the Solutions of Brilliant’s Composite Mathematics Class 8 Math Book, Chapter 18, Statistics. Here students can easily find step by step solutions of all the problems for Statistics, Exercise 18.1, 18.2 and 18.3 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.

**Statistics Exercise 18.1 Solution**

**Question no – (4) **

**Solution :**

Required frequency distribution table,

Marks (x) |
Number of students (f ) |
F × x |

1 | 8 | 1 × 8 = 8 |

2 | 5 | 2 × 5 = 10 |

3 | 7 | 3 × 7 = 21 |

4 | 3 | 4 × 3 = 12 |

5 | 2 | 5 × 2 = 10 |

Total |
Σf = 25 | Σf × x = 61 |

**Question no – (8)**

**Solution :**

Marks (x) |
Number of students (f) |
F × x |

1 | 1 | 1 |

3 | 1 | 3 |

4 | 2 | 8 |

6 | 1 | 6 |

8 | 1 | 8 |

10 | 1 | 10 |

12 | 1 | 12 |

Total |
8 | 48 |

**∴** Arithmetic mean,

= Σf × x/Σf

= 48/8

= 6

Hence, the arithmetic mean will be 6

**Question no – (9)**

**Solution :**

Mean attendance,

= 1/6 (425 + 430 + 408 + 400 + 423 + 410)

= 1/6 (2496)

= 416

Hence, the mean attendance will be 416

**Question no – (10)**

**Solution :**

Average score,

= 1/11 (3 + 20 + 0 + 15 + 16 + 30 + 61 + 35 + 20 + 6 + 5)

= 1/11 (231)

= 21

Thus, the average score will be 21

**Question no – (11)**

**Solution :**

Arithmetic mean,

= 1/15 (34) + 24 + 24 + 24 + 22 + 17 + 30 + 34 + 24 + 30 + 24 + 22 + 32 + 28 + 22

= 1/15 (1155)

= 77

Therefore, the mean will be 77

**Question no – (14)**

**Solution :**

Mean = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8/8

= 30/8

= 4.5

Hence, the mean of first 8 natural number is 4.5

**Question no – (16)**

**Solution :**

Mean = 2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18/9

= 90/9

= 10

Therefore, the mean of first 9 natural number is 10

**Question no – (17)**

**Solution :**

Mean = 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17/8

= 80/8

= 10

Thus, the mean number will be 10

**Question no – (19)**

**Solution :**

3.4 + 3.6 + 4.2 + 3.6 + 4.5 + 3.9 + 4.1 + 3.8 + 4.5 + 4.4/10

= 40/10

= 4 kg.

Hence, the mean weight will be 4 kg.

**Question no – (22)**

**Solution :**

Pocket expense (x) |
Number of students (f ) |
F × x |

8 | 15 | 120 |

10 | 12 | 120 |

12 | 13 | 150 |

15 | 25 | 375 |

20 | 15 | 300 |

Total |
80 | 1051 |

**∴** Mean

= 1051/80

= 13.39

Therefore, their mean pocket expenses will be 13.39

**Statistics Exercise 18.3 all Questions Solution : **

**Question no – (3) **

**Solution :**

**(i)** Class size,

= 440 – 420

= 20

**(ii)** 10

**(iii)** 5 + 20 = 25

**(iv)** The number of workers is maximum in the internal 500 – 520.

**(v)** 20

**(vi)** 560 – 580 The number of such workers is 5.

**(vii)** The total number of workers is 120.

**Question no – (4) **

**Solution :**

**(i)** Class size,

= 20 – 15

= 5

**(ii)** The crank mark on x – axis means that owing to lack of space this small distance represent.

0 – 15.

**(iii)** In the age group 15 – 20, maximum person are literate. Their number is 40.

**(iv)** The number of literate person above the age of 35 years is 35.

**(v)** In the age group 40 – 45 the number of literate persons is minimum

= Their number is 5.

**(vi)** The total number of literate persons is 165.

**(vii)** 1 cm = 1 person

**Previous Chapter Solution : **