Question

If mean of the following distribution is 24, find the value of a: [4] Marks 0-10 10-20 20-30 30-40 40-50 Number of students 7 a 8 10 5

Answer 1

Marks Average Marks  Number of Students  

0−10  5   5

10−20  15   8

20−30  25   15

30−40   53   16

40−50   45   6

Mean =  

5+8+15+16+6

5×5+15×8+28×15+35×16+45×6

​  

 

=  

50

1350

​  

 

=27

So mean deviation about mean =  

5+8+15+16+6

5×∣5−27∣+8×∣15−27∣+15×∣25−27∣+16×∣35−27∣+6×∣45−27∣

​  

 

=  

50

472

​  

 

=9.44