Erika's mother is 5 times as old as her. Erika will be 9 years old in 3 years' time. In how many years' time will Erika's age be 70% that of her mother's?
| |
Erika's mother |
Erika |
Difference |
Before
(now) |
5x3 =
15 u |
1x3 =
3 u |
4x3 =
12 u |
| Change 1 |
+ 3 |
+ 3 |
|
| After 1 |
|
9 |
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
10x4 =
40 u |
7x4 =
28 u |
3x4 =
12 u |
70% =
70100 =
710 Erika's mother : Erika = 10 : 7
The difference in age between Erika's mother and Erika always remains the same. Make the difference in age between Erika's mother and Erika the same. LCM of 4 and 3 is 12.
3 u + 3 = 9
3 u = 9 - 3
3 u = 6
1 u = 6 ÷ 3 = 2
Number of years' time when Erika's age will be 70% that of her mother's
= 40 u - 33
= 40 x 2 - 33
= 80 - 33
= 47
Answer(s): 47
