Last year, Ben was 3 times as old as his son, Sam. This year, their total age is 42 years old. How old will Sam be when Ben is 2 times as old as him?
| |
Ben |
Sam |
Difference |
Total |
| Before |
3x1 =
3 u |
1x1 =
1 u |
2x1 =
2 u |
|
| Change 1 |
+ 1 |
+ 1 |
|
|
| After 1 |
3 u + 1 |
1 u + 1 |
|
42 |
| Change |
+ ? |
+ ? |
|
|
After 2 |
2x2 =
4 u |
1x2 =
2 u |
1x2 =
2 u |
|
The difference in Ben's age and his son's age always remains unchanged. Make the difference in age the same. LCM of 2 and 1 is 2.
Total age of Ben and his son this year
= 3 u + 1 + 1 u + 1
= 4 u + 2
4 u + 2 = 42
4 u = 42 - 2
4 u = 40
1 u = 40 ÷ 4 = 10
Ben's age when Ben is 2 times as old as him
= 2 u
= 2 x 10
= 20
Answer(s): 20
