Billy's uncle is 3 times as old as him. His uncle will be 36 years old in 12 years' time. In how many years' time will Billy's age be 80% that of his uncle's?
| |
Billy's uncle |
Billy |
Difference |
Before
(now) |
3x1 =
3 u |
1x1 =
1 u |
2x1 =
2 u |
| Change 1 |
+ 12 |
+ 12 |
|
| After 1 |
36 |
|
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
5x2 =
10 u |
4x2 =
8 u |
1x2 =
2 u |
80% =
80100 =
45 Billy's uncle : Billy = 5 : 4
The difference in age between Billy's uncle and Billy always remains the same. Make the difference in age between Billy's uncle and Billy the same. LCM of 2 and 1 is 2.
3 u + 12 = 36
3 u = 36 - 12
3 u = 24
1 u = 24 ÷ 3 = 8
Number of years' time when Billy's age will be 80% that of his uncle's
= 10 u - 36
= 10 x 8 - 36
= 80 - 36
= 44
Answer(s): 44
