The ratio of gold to black stamps that Gabby had was 4 : 3. The cost of each of the gold stamps was $5 and the cost of each of the black stamps was $10. Gabby sold 25% of the gold stamps and the total cost of the unsold stamps was $405. How many black stamps did she have left?
| |
Gold stamps |
Black stamps |
| Before |
4 u |
3 u |
| Change |
- 1 u |
|
| After |
3 u |
3 u |
Number of gold stamps sold
= 25% x 4 u
=
25100 x 4 u
= 1 u
| |
Gold stamps |
Black stamps |
Total |
| Number |
3 u |
3 u |
|
| Value |
$5 |
$10 |
|
| Total value |
15 u |
30 u |
$405 |
Total cost of unsold stamps
= 15 u + 30 u
= 45 u
45 u = 405
1 u = 405 ÷ 45 = 9
Number of black stamps that Gabby had left
= 30 u
= 30 x 9
= 270
Answer(s): 270
