Multiple choice

The ratio of father's age to his son's age is 7 : 5. The product of their ages is 875. The ratio of their ages after 7 years will be

  1. $3 : 2$
  2. $21 : 16$
  3. $21 : 8$
  4. $27 : 16$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let father's age = 7x, son's age = 5x. Product = 35x² = 875, so x² = 25, x = 5. Current ages: father = 35, son = 25. After 7 years: father = 42, son = 32. Ratio = 42:32 = 21:16. Always find the actual ages first using the product information.