The ratio of Billy's age to Zeph's age is 5 : 3. Next year, their average age will be 13. How old will Billy be in 7 years' time?
| |
Billy |
Zeph |
Total |
| Before |
5 u |
3 u |
24 |
| Change |
+ 1 |
+ 1 |
|
| After |
5 u + 1 |
3 u + 1 |
26 |
Total age of Billy and Zeph this year
= 5 u + 3 u
= 8 u
Total age of Billy and Zeph this year
= 2 x 13 - 1 - 1
= 26 - 2
= 24
8 u = 24
1 u = 24 ÷ 8 = 3
Billy's age in 7 years' time
= 5 u + 7
= 5 x 3 + 7
= 15 + 7
= 22
Answer(s): 22
