SOLUTION: Tom's father is three times as old as Tom. Four years ago Tom's father was four times as old as Tom. How old is Tom?

Let:

Tom's age now = T

>>...Tom's father is three times as old as Tom...<<

TRANSLATION:

Tom's father's age now = 3T

Then 

Tom's age four years ago = T-4

and

Tom's father's age four years ago = 3T-4

>>... Four years ago Tom's father was four times as old as Tom...<<

TRANSLATION:

Tom's father's age four years ago = 4 times Tom's age 4 years ago

                             3T-4 = 4(T-4)

                             3T-4 = 4T-16

                            3T-4T = 4-16

                               -T = -12

                                T = 12

Check:

Tom is 12 years old.  His father is 3 times as old as Tom, or 36.

Four years ago, Tom was 8 and his father was 32.  So indeed Tom's father

was four times as old as Tom was then.



Edwin