Bobby's age is
38 of his grandfather's. His grandfather will be 83 years old in 11 years' time. In how many years' time will Bobby's age be
12 that of his grandfather's?
| |
Bobby |
His grandfather |
Difference |
| Before |
3x1 =
3 u |
8x1 =
8 u |
5x1 =
5 u |
| Change 1 |
+ 11 |
+ 11 |
|
| After |
|
83 |
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
1x5 =
5 u |
2x5 =
10 u |
1x5 =
5 u |
The age difference between Bobby and his grandfather remains unchanged.
LCM of 5 and 1 is 5.
8 u + 11 = 83
8 u = 83 - 11
8 u = 72
1 u = 72 ÷ 8 = 9
Number of years' time when Bobby's age will be
12 that of his grandfather's age
= 5 u - 3 u
= 2 u
= 2 x 9
= 18
Answer(s): 18
