Brandon's age is
38 of his grandfather's. His grandfather will be 100 years old in 20 years' time. In how many years' time will Brandon's age be
12 that of his grandfather's?
| |
Brandon |
His grandfather |
Difference |
| Before |
3x1 =
3 u |
8x1 =
8 u |
5x1 =
5 u |
| Change 1 |
+ 20 |
+ 20 |
|
| After |
|
100 |
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
1x5 =
5 u |
2x5 =
10 u |
1x5 =
5 u |
The age difference between Brandon and his grandfather remains unchanged.
LCM of 5 and 1 is 5.
8 u + 20 = 100
8 u = 100 - 20
8 u = 80
1 u = 80 ÷ 8 = 10
Number of years' time when Brandon's age will be
12 that of his grandfather's age
= 5 u - 3 u
= 2 u
= 2 x 10
= 20
Answer(s): 20
