Multiple choice

Five years ago. the ratio of the of a father and his son was 7:2. Five years hence, the ratio will become 9:4. What is the father's current age?

  1. 35 years

  2. 40 years

  3. 45 years

  4. 50 years
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let the father's and son's ages five years ago be 7k and 2k. Five years hence, their ages are 7k + 10 and 2k + 10, whose ratio is 9:4. Solving 4(7k + 10) = 9(2k + 10) gives k = 5, so the father's current age is 7(5) + 5 = 40 years.

AI explanation

Let the father's age five years ago be 7x and the son's age be 2x. Five years hence, their ages will be 7x plus 10 and 2x plus 10, yielding the proportional equation (7x plus 10) divided by (2x plus 10) equals 9 divided by 4. Cross-multiplying gives 28x plus 40 equals 18x plus 90, which simplifies to 10x equals 50, so x equals 5. The father's present age is 7x plus 5, which is 40 years.

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