The average age of 5 children of a family is 15 years. Average age of children together with their father and mother is 25 years. If the father is older than the mother by 4 years, then find the age of mother (in years).

48

Sum of ages of whole family = 7 x 25 =175

Sum of ages of Children = 5 x 15 =75

So,

Sum of ages of parents  = 100

If  mother's age is x then father's age is x+4

So, 2x + 4 = 100

Mother's age (x) = 48 years