Paul is 12. His father is 33. How many years ago was the father 4 times as old as the son?
Paul x years ago ---> 12-x
father x yrs ago ----> 33-x
when was 33-x = 4(12-x) ?
33-x = 48 - 4x
3x = 15
x = 5
Check:
Five years ago Paul was 12-5 = 7
Father was 33-5 = 28
isn't 28 = 4x7 ?