Bobby's age is
27 of his grandaunt's. His grandaunt will be 75 years old in 5 years' time. In how many years' time will Bobby's age be
12 that of his grandaunt's?
| |
Bobby |
His grandaunt |
Difference |
| Before |
2x1 =
2 u |
7x1 =
7 u |
5x1 =
5 u |
| Change 1 |
+ 5 |
+ 5 |
|
| After |
|
75 |
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
1x5 =
5 u |
2x5 =
10 u |
1x5 =
5 u |
The age difference between Bobby and his grandaunt remains unchanged.
LCM of 5 and 1 is 5.
7 u + 5 = 75
7 u = 75 - 5
7 u = 70
1 u = 70 ÷ 7 = 10
Number of years' time when Bobby's age will be
12 that of his grandaunt's age
= 5 u - 2 u
= 3 u
= 3 x 10
= 30
Answer(s): 30
