how old is a boy if his years is average of his mother's years and his father is five years older than his mother and their age altogether is hundred years.
I took the average of his mother's age to mean his mother's age, or his mother being twice his age, which somehow doesn't make sense since an average
usually includes at least 2 expressions. Nonetheless, that's how I arrived at the above answer.
You need to better state a math problem if your desire is to get sensible answers, unless of course that's the way the problem was stated to you, which I somewhat doubt!