Mark's mother is 7 times as old as him. His mother will be 38 years old in 10 years' time. In how many years' time will Mark's age be 70% that of his mother's?
| |
Mark's mother |
Mark |
Difference |
Before
(now) |
7x1 =
7 u |
1x1 =
1 u |
6x1 =
6 u |
| Change 1 |
+ 10 |
+ 10 |
|
| After 1 |
38 |
|
|
| Change 2 |
+ ? |
+ ? |
|
| After 2 |
10x2 =
20 u |
7x2 =
14 u |
3x2 =
6 u |
70% =
70100 =
710 Mark's mother : Mark = 10 : 7
The difference in age between Mark's mother and Mark always remains the same. Make the difference in age between Mark's mother and Mark the same. LCM of 6 and 3 is 6.
7 u + 10 = 38
7 u = 38 - 10
7 u = 28
1 u = 28 ÷ 7 = 4
Number of years' time when Mark's age will be 70% that of his mother's
= 20 u - 38
= 20 x 4 - 38
= 80 - 38
= 42
Answer(s): 42
