Let us denote the years of Mary with M and the years that Al have with A. We know that the sum of Mary and Al's age is 48. So, we can write: M+A=48 (1) We also know that twelve years ago, Mary was twice as old as Al.
So we can write: M-12=2*A (2) From the first equation (1): M=48-A Let put this in the second equation: 48-A-12=2A 36=3A A=12 M=48-12=36
