Number Of Earning People

What was the question? 

Let's suppose there are m men, w women and c children.

As per given data,

m + w + c = 20   ......(1)

3m + 1.5w + 0.5c = 20   .....(2)

Multiply equation (1) by 3 and then subtracting from (2), we get,

5m + 2w = 20.

For m and w to be whole numbers, m must be 2 and w must be 5 satisfying above equation.

Hence, from (1),

c = 20 - 2 - 5 = 13.

 
To conclude, there are 2 men, 5 women and 13 children.