Question

Marks no.of student
10-20 20
20-30 25
30-40 15
40-50 10
50-60 20
60-70 10
*find mean*

Answer 1

Mean = sum of observations /number of observations
= 20 + 25 + 15 + 10 + 20 + 10 /6
= 100/6
= 91.66

Hope this will help you..

Answer 2

Take 45 assumed mean
Fiui would be -60-50-15+0=20+20
=85
Fi is 100
45+85/100*10
45+17/2

53.5 is the mean