Question 7352
<font face = "courier new">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?</font>
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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