Anjali's mother is four times as old as Anjali. In 10 years the mother will be only twice as old as Anjali. Find the MOTHER'S present age (in years).

Let Anjali be a years old, so her mother is $4a$. In 10 years: $4a+10=2(a+10)=2a+20$ → $2a=10$ → $a=5$, so the mother is $4\times 5=20$. Check: in 10 years they will be 30 and 15, and $30=2\times 15$. The traps 5, 30 and 15 are Anjali's present age, the mother's future age and Anjali's future age.