Multiple choice

The average of present age of A and B is 21 years. After 3 years, the ratio of ages of A and B will be 7:5. What will be age of A after 4 years from present?

  1. 29 years

  2. 27 years

  3. 22 years

  4. 31 years

  5. None of these
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A Correct answer
Explanation

Let the present ages of A and B be a and b years. Their average is 21, so a + b = 42. After 3 years, the ratio becomes 7:5, meaning (a+3)/(b+3) = 7/5. Solving: 5(a+3) = 7(b+3) gives 5a - 7b = 6. Substituting b = 42-a yields 5a - 7(42-a) = 6, so 12a = 300 and a = 25. After 4 years, A's age will be 25 + 4 = 29 years.

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