The ratio of the number of green buttons to red buttons is 5 : 3. After David gives away 10 green buttons and buys another 90 red buttons, there is equal number of green buttons and red buttons. How many buttons does David have now?
| |
Green |
Red |
| Before |
5 u |
3 u |
| Change |
- 10 |
+ 90 |
| After |
5 u - 10 |
3 u + 90 |
The number of green buttons and red buttons in the end is the same.
5 u - 10 = 3 u + 90
5 u - 3 u = 90 + 10
2 u = 100
1 u = 100 ÷ 2 = 50
Number of buttons that David has now
= 5 u - 10 + 3 u + 90
= 5 u + 3 u - 10 + 90
= 8 u + 80
= 8 x 50 + 80
= 400 + 80
= 480
Answer(s): 480
