Question

Question 7 Find the mean and variance for the following frequency distribution.




Classes Frequencies



0-30 2


30-60 3


60-90 5


90-120 10


120-150 3


150-180 5


180-210 2


Class X1 - Maths -Statistics Page 371

Answer 1

we have to use the formula for finding mean is
$Mean(\overline{x})=A+ \frac{\sum{f_id_i}}{\sum{f_i}}\times\:h$
where , A is assumed mean,
h is the class interval .
and for finding variance , we have use the formula is
$variance (\sigma)=[\frac{\sum{f_id_i^2}}{\sum{f_i}}-(\frac{\sum{f_id_i}}{\sum{f_i}})^2]\times\:h^2$

see attachment ,
we get
mean = 107 and variance = 2276