The ratio of John's age to Valen's age is 2 : 1. Next year, their average age will be 10. How old will John be in 9 years' time?
| |
John |
Valen |
Total |
| Before |
2 u |
1 u |
18 |
| Change |
+ 1 |
+ 1 |
|
| After |
2 u + 1 |
1 u + 1 |
20 |
Total age of John and Valen this year
= 2 u + 1 u
= 3 u
Total age of John and Valen this year
= 2 x 10 - 1 - 1
= 20 - 2
= 18
3 u = 18
1 u = 18 ÷ 3 = 6
John's age in 9 years' time
= 2 u + 9
= 2 x 6 + 9
= 12 + 9
= 21
Answer(s): 21
