Ten years ago the ages of Kavita and her mother were in the ratio 1 : 7. Ten years from now their ages will be in the ratio 5 : 11. Kavita's present age (in years) is:

Let the ages ten years ago be $x$ and $7x$. Twenty years later — that is, ten years from now — they are $x+20$ and $7x+20$, so $(x+20)/(7x+20)=5/11$ → $11x+220=35x+100$ → $24x=120$ → $x=5$. Kavita was 5 then, so she is 15 now (her mother is 45). Answering 5 stops at her age ten years ago.