Billy's current age is 9 times as old as Charlie's age years ago. Today, Charlie's age is Billy's age the same number of years ago. How old is Charlie's age now if the total of their current age is 28?
| |
Billy |
Charlie |
Difference |
Total |
| Before |
1 p |
1 u |
1 p - 1 u |
|
| Change |
+ ? |
+ ? |
|
|
| After |
9 u |
1 p |
9 u - 1 p |
28 |
Total age of Billy and Charlie today = 9 u + 1 p
9 u + 1 p = 28 --- (1)
The difference in Billy's age and Charlie's age remains the same.
9 u - 1 p = 1 p - 1 u
9 u + 1 u = 1 p + 1 p
10 u = 2 p
5 u = 1 p
Substitute 1 p = 5 u into (1).
9 u + 1 p = 28
9 u + 5 u = 28
14 u = 28
1 u = 28 ÷ 14 = 2
Billy's age now
= 28 - 9 u
= 28 - 9 x 2
= 28 - 18
= 10
Answer(s): 10
