SOLUTION: John is 12, Peter is 3. How many years will it take for John to be 3 times as old as Peter?

In x years.


In x years, John will be 12+x years old;  Peter will be 3+x years old.


John will be 3 times as old as Peter:


    12 + x = 3*(3 + x).


Simplify and find x


    12 + x = 9 + 3x

    12 - 9 = 3x - x

       3   = 2x

       x    = 3/2 years.


When the age problem has no solution in integer numbers, it is TRADITIONALLY considered as DEFECTIVE.