The ratio of the number of blue stamps to green stamps is 5 : 3. After David gives away 20 blue stamps and buys another 70 green stamps, there is equal number of blue stamps and green stamps. How many stamps does David have now?
| |
Blue |
Green |
| Before |
5 u |
3 u |
| Change |
- 20 |
+ 70 |
| After |
5 u - 20 |
3 u + 70 |
The number of blue stamps and green stamps in the end is the same.
5 u - 20 = 3 u + 70
5 u - 3 u = 70 + 20
2 u = 90
1 u = 90 ÷ 2 = 45
Number of stamps that David has now
= 5 u - 20 + 3 u + 70
= 5 u + 3 u - 20 + 70
= 8 u + 50
= 8 x 45 + 50
= 360 + 50
= 410
Answer(s): 410
