Sam's auntie is 3 times as old as him. His auntie will be 31 years old in 7 years' time. In how many years' time will Sam's age be 80% that of his auntie's?
| |
Sam's auntie |
Sam |
Difference |
Before
(now) |
3x1 =
3 u |
1x1 =
1 u |
2x1 =
2 u |
| Change 1 |
+ 7 |
+ 7 |
|
| After 1 |
31 |
|
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
5x2 =
10 u |
4x2 =
8 u |
1x2 =
2 u |
80% =
80100 =
45 Sam's auntie : Sam = 5 : 4
The difference in age between Sam's auntie and Sam always remains the same. Make the difference in age between Sam's auntie and Sam the same. LCM of 2 and 1 is 2.
3 u + 7 = 31
3 u = 31 - 7
3 u = 24
1 u = 24 ÷ 3 = 8
Number of years' time when Sam's age will be 80% that of his auntie's
= 10 u - 31
= 10 x 8 - 31
= 80 - 31
= 49
Answer(s): 49
