Question

The ratio of the present ages of a father and son is 7 : 2. After 10 years, the ratio becomes 9 : 4. The present age of the father is:

• A. 35 years
• B. 42 years
• C. 28 years
• D. 40 years

Answer 1

The Correct Option is A

Step 1: Let ages be \(7x\) and \(2x\). After 10 years: \(\dfrac{7x+10}{2x+10} = \dfrac{9}{4}\).
Step 2: \(4(7x+10) = 9(2x+10) \Rightarrow 28x+40 = 18x+90 \Rightarrow 10x = 50 \Rightarrow x = 5\).
Step 3: Father's present age \(= 7x = 35\) years.

Quick Tip: Add the same time to every age, then re-apply the new ratio.