Betty's mother is 4 times as old as her. Betty will be 10 years old in 4 years' time. In how many years' time will Betty's age be 60% that of her mother's?
| |
Betty's mother |
Betty |
Difference |
Before
(now) |
4x2 =
8 u |
1x2 =
2 u |
3x2 =
6 u |
| Change 1 |
+ 4 |
+ 4 |
|
| After 1 |
|
10 |
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
5x3 =
15 u |
3x3 =
9 u |
2x3 =
6 u |
60% =
60100 =
35 Betty's mother : Betty = 5 : 3
The difference in age between Betty's mother and Betty always remains the same. Make the difference in age between Betty's mother and Betty the same. LCM of 3 and 2 is 6.
2 u + 4 = 10
2 u = 10 - 4
2 u = 6
1 u = 6 ÷ 2 = 3
Number of years' time when Betty's age will be 60% that of her mother's
= 15 u - 28
= 15 x 3 - 28
= 45 - 28
= 17
Answer(s): 17
