The present ages of three sisters are in the ratio $2 : 3 : 5$. Seven years ago, the sum of their ages was 39 years. How old is the eldest sister now?

Explanation

1. 01

   Present ages $2k, 3k, 5k$: total $10k$.

2. 02

   Seven years ago each was 7 younger, so the total was $10k - 21 = 39$.

3. 03

   $10k = 60$, $k = 6$: ages 12, 18, 30.

4. 04

   Eldest = 30 years.