When Shiyun was 42 years old, her daughter was 4 times her son's age. Shiyun would be twice her daughter's age when her son was 21 years old. How old would Shiyun be when her son was 5 years old?
|
Shiyun |
Daughter |
Son |
Before |
42 |
4 u |
1 u |
Change |
+ ? |
+ ? |
+ ? |
After |
2 p |
1 p |
21 |
The difference in the ages between Shiyun and her daughter remains unchanged.
Difference in Shiyun's and her daughter's ages at first
42 - 4 u = 2 p - 1 p
42 - 4 u =
1 p --- (1)
The difference in the ages between her daughter and her son remains unchanged.
Difference in her daughter's and her son's ages at first
4 u - 1 u = 1 p - 21
3 u + 21 =
1 p --- (2)
Make p the same.
(1) = (2)
42 - 4 u = 3 u + 21
3 u + 4 u = 42 - 21
7 u = 21
1 u = 21 ÷ 7 = 3
Age difference between Shiyun and her son
= 42 - 1 u
= 42 - 3
= 39
Shiyun's age when her son was 5 years old
= 39 + 5
= 44
Answer(s): 44