Sarah's auntie is 3 times as old as her. Sarah will be 13 years old in 4 years' time. In how many years' time will Sarah's age be 70% that of her auntie's?
| |
Sarah's auntie |
Sarah |
Difference |
Before
(now) |
3x3 =
9 u |
1x3 =
3 u |
2x3 =
6 u |
| Change 1 |
+ 4 |
+ 4 |
|
| After 1 |
|
13 |
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
10x2 =
20 u |
7x2 =
14 u |
3x2 =
6 u |
70% =
70100 =
710 Sarah's auntie : Sarah = 10 : 7
The difference in age between Sarah's auntie and Sarah always remains the same. Make the difference in age between Sarah's auntie and Sarah the same. LCM of 2 and 3 is 6.
3 u + 4 = 13
3 u = 13 - 4
3 u = 9
1 u = 9 ÷ 3 = 3
Number of years' time when Sarah's age will be 70% that of her auntie's
= 20 u - 31
= 20 x 3 - 31
= 60 - 31
= 29
Answer(s): 29
