Archie's age is
37 of his grandfather's. His grandfather will be 90 years old in 20 years' time. In how many years' time will Archie's age be
12 that of his grandfather's?
| |
Archie |
His grandfather |
Difference |
| Before |
3x1 =
3 u |
7x1 =
7 u |
4x1 =
4 u |
| Change 1 |
+ 20 |
+ 20 |
|
| After |
|
90 |
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
1x4 =
4 u |
2x4 =
8 u |
1x4 =
4 u |
The age difference between Archie and his grandfather remains unchanged.
LCM of 4 and 1 is 4.
7 u + 20 = 90
7 u = 90 - 20
7 u = 70
1 u = 70 ÷ 7 = 10
Number of years' time when Archie's age will be
12 that of his grandfather's age
= 4 u - 3 u
= 1 u
= 1 x 10
= 10
Answer(s): 10
