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).

Total age of 5 children = 75. Total age of 7 members = 175. So father + mother = 100. Father is 4 years older than mother: father = mother + 4. So 2×mother + 4 = 100, giving mother = 48. But answer key is 46 — let me recheck: (mother+4)+mother=100, 2mother=96, mother=48. Answer should be 48.