Last year, Riordan was 5 times as old as his son, Ivan. This year, their total age is 80 years old. How old will Riordan be when he is 3 times as old as Ivan?
| |
Riordan |
Ivan |
Difference |
Total |
| Before |
5x1 =
5 u |
1x1 =
1 u |
4x1 =
4 u |
|
| Change 1 |
+ 1 |
+ 1 |
|
|
| After 1 |
5 u + 1 |
1 u + 1 |
|
80 |
| Change |
+ ? |
+ ? |
|
|
After 2 |
3x2 =
6 u |
1x2 =
2 u |
2x2 =
4 u |
|
The difference in Ben's age and his son's age always remains unchanged. Make the difference in age the same. LCM of 4 and 2 is 4.
Total age of Riordan and his son this year
= 5 u + 1 + 1 u + 1
= 6 u + 2
6 u + 2 = 80
6 u = 80 - 2
6 u = 78
1 u = 78 ÷ 6 = 13
Riordan's age when he is 3 times as old as Ivan
= 6 u
= 6 x 13
= 78
Answer(s): 78
