Question

Mike is three times as old as his little sister, Mary. In 4 years, he will be twice as old as Mary. How old is Mary?

Answer 1

Let Mary be x years old
Mike is 3x years old
In 4 years Mary would be (x+4)yr old
 and Mike would be 2(x+4)
 Mikes age after 4 years  3x + 4 = 2(x+4)
                                  ⇒ x = 4
Mary is 4 years old