The ratio of black to green stamps that Gem had was 5 : 4. The cost of each of the black stamps was $5 and the cost of each of the green stamps was $9. Gem sold 40% of the black stamps and the total cost of the unsold stamps was $357. How many black stamps did she have left?
| |
Black stamps |
Green stamps |
| Before |
5 u |
4 u |
| Change |
- 2 u |
|
| After |
3 u |
4 u |
Number of black stamps sold
= 40% x 5 u
=
40100 x 5 u
= 2 u
| |
Black stamps |
Green stamps |
Total |
| Number |
3 u |
4 u |
|
| Value |
$5 |
$9 |
|
| Total value |
15 u |
36 u |
$357 |
Total cost of unsold stamps
= 15 u + 36 u
= 51 u
51 u = 357
1 u = 357 ÷ 51 = 7
Number of black stamps that Gem had left
= 15 u
= 15 x 7
= 105
Answer(s): 105
