Question 612951
Let S = Sean's present age and B = his brother's present age, then:
1) S-5 = 3(B-5) "Five years ago, Sean was three times as old as his brother (was five years ago)."
2) S = 2B "Today Sean is twice as old as his brother."
Substitute equation 2) into equation 1) to get:
(2B)-5 = 3(B-5) Simplify.
2B-5 = 3B-15 Subtract 2B from both sides.
-5 = B-15 Now add 15 to both sides.
10 = B and S = 2(10) = 20.
Sean is 20 years old and his brother is 10 years old, so Sean is 10 years older than his brother.