# CBSE Class 10 Maths 2018 Question Paper Solution | Q 30A

###### CBSE Solved Question Paper 4 Mark | Statistics

A relatively easy four mark question from the chapter Statistics. Two steps to arrive at the answer. The calculation is also easy for this question.

Question 30A: The mean of the following distribution is 18. Find the frequency f of the class 19 – 21.

Class 11 - 13 13 - 15 15 - 17 17 - 19 19 - 21 21 - 23 23 - 25
Frequency 3 6 9 13 f 5 4

## NCERT Solution to Class 10 Maths

### Explanatory Answer | CBSE Class 10 Math 2018 Paper Q 30A

#### Step 1: Compute fixi for the given data

Class Frequency fi Class Mean xi fixi
11 - 13 3 12 36
13 - 15 6 14 84
15 - 17 9 16 144
17 - 19 13 18 234
19 - 21 f 20 20f
21 - 23 5 22 110
23 - 25 4 24 96

Σfi = 40 + f
Σfixi = (704 + 20f)

#### Step 2: Compute Frequency of Class Interval 19 - 21

Mean x = $$frac{Σf_i x_i}{Σf_i}$ 18 = $\frac{704 + 20f}{40 + f}$ 18$40 + f) = 704 + 20f
720 + 18f = 704 + 20f
16 = 2f
f = 8

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