SOLUTION: The sum of two digits of a 2-digit # is 12. If the units digit is 3 times the tens digit, find the #

Question 332590: The sum of two digits of a 2-digit # is 12. If the units digit is 3 times the tens digit, find the #
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
It's 39.
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Since it adds to 12 and the 1's is 3x the 10's, both digits have to be multiples of 3.
39 is the only possibility
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The hard way:
t = 10s digit, u = 1s digit
t + u = 12
u = 3t
Sub for u in the 1st eqn
t + 3t = 12
4t = 12
t = 3
u = 9
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