Discussion

The sum of ages of a father and a daughter is 80 years now. If 10 years ago the ratio was 2:1, then after 10 years the ratio of their ages will be:

Answer: A

After 10 years the ratio will be 3:2.

Let the father's age be \(F\) and the daughter's \(D\), so \(F + D = 80\). Ten years ago their ages were in the ratio 2:1:

\[ \begin{aligned} F - 10 &= 2(D - 10) \\ (F - 10) + (D - 10) &= 60 \\ 3(D - 10) &= 60 \\ D &= 30,\ F = 50 \end{aligned} \]

After 10 years they will be 60 and 40, a ratio of 60:40 = 3:2.

5:3 is their present ratio (50:30), the usual slip of forgetting to add the 10 years.

No comment is present. Be the first to comment.

Loading…