Question:

For the frequency distribution (class: 0-10, 10-20, 20-30, 30-40, 40-50; frequency: 2,3,x,5,4) with mean 28, the variance is ________.

Step-by-Step Solution

Key Concept: Use class midpoints. Mean$=28$ gives $x=6$ (total $N=20$). Compute $\sigma^2=\frac{\sum f_i(x_i-28)^2}{20}$.

$\sigma^2=151$.

Correct Answer: 151