Question

Question 8 Find the mean and variance for the following frequency distribution.




Classes Frequencies



0-10 5


10-20 8


20-30 15


30-40 16


40-50 6



Class X1 - Maths -Statistics Page 372

Answer 1

we have to use the formula for finding mean of given table is
$mean(\overline{x})=A+\frac{\sum{f_id_i}}{\sum{f_i}}\times\:h$

where A is assumed mean and h is class interval .
and for finding variance, we have to use the formula is
$variance (\sigma)=[\frac{\sum{f_id_i^2}}{\sum{f_i}}-(\frac{ \sum{f_id_i}}{\sum{f_i}})^2]\times\:h^2$
hence, after solving
we get , mean = 27 and variance = 132