Oscar is 5 times as old as his brother. In 18 years' time, Oscar will be 3 years less than twice of his brother's age. How old was Oscar 5 years ago?
|
Oscar |
Oscar's brother |
Difference |
Before |
5 u |
1 u |
4 u |
Change |
+ 18 |
+ 18 |
|
After |
2 p - 3 |
1 p |
1 p - 3 |
Difference in their ages at first
= 5 u - 1 u
= 4 u
Difference in their ages in the end
= 2 p - 3 - 1 p
= 1 p - 3
The difference in their ages remains unchanged.
4 u = 1 p - 3
4 u + 3 =
1 p --- (1)
Age of Oscar's brother in 18 years' time
= 1 u + 18
1 u + 18 =
1 p --- (2)
(1) = (2)
4 u + 3 = 1 u + 18
4 u - 1 u = 18 - 3
3 u = 15
1 u = 15 ÷ 3 = 5
Oscar's current age
= 5 u
= 5 x 5
= 25
Oscar's age 5 years ago
= 25 - 5
= 20
Answer(s): 20