The ratio of black to red stamps that Roshel had was 5 : 2. The cost of each of the black stamps was $5 and the cost of each of the red stamps was $7. Roshel sold 60% of the black stamps and the total cost of the unsold stamps was $144. How many red stamps did she have left?
| |
Black stamps |
Red stamps |
| Before |
5 u |
2 u |
| Change |
- 3 u |
|
| After |
2 u |
2 u |
Number of black stamps sold
= 60% x 5 u
=
60100 x 5 u
= 3 u
| |
Black stamps |
Red stamps |
Total |
| Number |
2 u |
2 u |
|
| Value |
$5 |
$7 |
|
| Total value |
10 u |
14 u |
$144 |
Total cost of unsold stamps
= 10 u + 14 u
= 24 u
24 u = 144
1 u = 144 ÷ 24 = 6
Number of red stamps that Roshel had left
= 14 u
= 14 x 6
= 84
Answer(s): 84
