Question 185872
Mary, who is sixteen years old, is four times as old as her brother. How old will Mary be when she is twice as old as her brother?

If Mary is 16 and this is 4 times as old as her brother, then we can say that her brother is 4 years old.

Let M = Mary's age when she is 2x as old as her brother.

16/M = 4/8

4M = 128

M = 128/4

M = 32