#### Calculate the mean of the scores of 20 students in a mathematics test : Marks 10-20 20-30 30-40 40-50 50-60 Number of students 2 4 7 6 1

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)
 Marks xi No.of students fi fixi 10-20 15 2 30 20-30 25 4 100 30-40 35 7 245 40-50 45 6 270 50-60 55 1 55

$\sum f_{i}= 20$      $\sum f_{i}x_{i}= 700$

$mean\left ( \bar{x} \right )= \frac{\sum f_{i}x_{i}}{\sum f_{i}}= \frac{700}{20}= 35$