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

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.

Video Explanation

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

Step 1: Compute f_ix_i for the given data

Σf_i = 40 + f
Σf_ix_i = (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