On average how much time did each of the last 40 people spend doing voluntary work?

Question

30 charity workers gave an average of three hours of their time per month doing voluntary work.

With the success of the project, a further 40 volunteers were recruited and the average hours given per month by all the volunteers rose to eight.

On average how much time did each of the last 40 people spend doing voluntary work?

Answer 1

30 workers time taken be x
40 workers time taken be y
Acc to first condition
x/30 = 3
x=90
Acc to second condition
x+y/70=8
90+y/70=8
90+y = 560
y=470
So average of 40 volunteers will be 470/40 =47/4 = 11.75