David's age is
25 of his grandmother's. His grandmother will be 58 years old in 13 years' time. In how many years' time will David's age be
23 that of his grandmother's?
| |
David |
His grandmother |
Difference |
| Before |
2x1 =
2 u |
5x1 =
5 u |
3x1 =
3 u |
| Change 1 |
+ 13 |
+ 13 |
|
| After |
|
58 |
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
2x3 =
6 u |
3x3 =
9 u |
1x3 =
3 u |
The age difference between David and his grandmother remains unchanged.
LCM of 3 and 1 is 3.
5 u + 13 = 58
5 u = 58 - 13
5 u = 45
1 u = 45 ÷ 5 = 9
Number of years' time when David's age will be
23 that of his grandmother's age
= 6 u - 2 u
= 4 u
= 4 x 9
= 36
Answer(s): 36
