The total mass of Abdul and his baby brother is 15.25kg. The mass of Abdul and his father is 72.25kg. The mass of Abdul's father is 13 times as heavy as Abdul's baby brother. What is Abdul's mass?

A+b=15.25

a+f=72.25, since f=13b

a+13b=72.25 so now we have two equation in two variables ...

a+13b=72.25 and a+b=15.25 so we can say:

(a+13b=72.25) - 13 (a+b=15.25)

a+13b-13a-13b=72.25-198.25

-12a=-126

a=10.5 kg

So Abdul's mass is 10.5 kilograms.