The difference between the ages of two persons is 10 years. Fifteen years ago, the elder one was twice as old as the younger one. The present age of the elder person is

$$\begin{gathered} \text{ Let the present age of the elder person be }x\text{ years. } \\ \text{ Then, the present age of the younger person }=(x-10)\text{ years. } \\ \because (x-15)=2(x-10-15) \\ \Rightarrow x=35 \\ \therefore \text{ the present age of the elder person is }35\text{ years. } \end{gathered}$$