Risa's auntie is 8 times as old as her. Risa will be 13 years old in 9 years' time. In how many years' time will Risa's age be 60% that of her auntie's?
| |
Risa's auntie |
Risa |
Difference |
Before
(now) |
8x2 =
16 u |
1x2 =
2 u |
7x2 =
14 u |
| Change 1 |
+ 9 |
+ 9 |
|
| After 1 |
|
13 |
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
5x7 =
35 u |
3x7 =
21 u |
2x7 =
14 u |
60% =
60100 =
35 Risa's auntie : Risa = 5 : 3
The difference in age between Risa's auntie and Risa always remains the same. Make the difference in age between Risa's auntie and Risa the same. LCM of 7 and 2 is 14.
2 u + 9 = 13
2 u = 13 - 9
2 u = 4
1 u = 4 ÷ 2 = 2
Number of years' time when Risa's age will be 60% that of her auntie's
= 35 u - 41
= 35 x 2 - 41
= 70 - 41
= 29
Answer(s): 29
