How much does Doug weigh?

Question

The average weight of Doug , his sister and his parents is
56 kg. The average weight of his mother and his sister is
52 kg. Doug's father weighs 3 times Doug's weight

Answer 1

Mum and sister weigh a total of 104 kg (2 x 52) therefore
Dad and Doug weigh a total of 120 kg (4 x 56) - 104
As dad weighs 3x and and Doug weighs x, 4x = 120 and x = 30
Therefore Doug weighs 30 kg and his dad weighs 90 kg.

Answer 2

x=doug
s=sister
m=mom
d=dad

1)( x+s+m+d)/4=56

2) (m+s)/2=56

3) d=3x

You will need to do a little substituting, but this might help.