The sum of the digits of a two-digit number is 15 and the difference between the digits is 3. What is the two-digit number?

A.    69   
B.    78
C.    96   
D.    Cannot be determined
E.    None of these
Ans: D

Explanation:

Let the ten's digit be x and unit's digit be y.
Then, x + y = 15 and x - y = 3   or   y - x = 3.
Solving x + y = 15   and   x - y = 3, we get: x = 9, y = 6.
Solving x + y = 15   and   y - x = 3, we get: x = 6, y = 9.
So, the number is either 96 or 69.
Hence, the number cannot be determined.