Calculate the mean of the following data Class 4-7 8-11 12-15 16-19 Frequency 5 4 9 10 :

Solution.  Here we calculate mean by following the given steps:

1. Find the mid point of each interval.
2. Multiply the frequency of each interval by its mid point.
3. Get the sum of all the frequencies (f) and sum of all the (fx)
4.  Now divide sum of (fx) by sum of (f)
 Class xi fi fi xi 4-7 5.5 5 275 8-11 9.5 4 38 12-15 13.5 9 121.5 16-19 17.5 10 175 $\sum f_{i}= 28$ $\sum f_{i}x_{i}= 362$

$mean\left ( \bar{x} \right )= \frac{\sum f_{i}x_{i}}{\sum f_{i}}= \frac{362}{28}= 12\cdot 93$