The ratio of silver to blue stamps that Mary had was 5 : 2. The cost of each of the silver stamps was $5 and the cost of each of the blue stamps was $10. Mary sold 40% of the silver stamps and the total cost of the unsold stamps was $140. How many blue stamps did she have left?
| |
Silver stamps |
Blue stamps |
| Before |
5 u |
2 u |
| Change |
- 2 u |
|
| After |
3 u |
2 u |
Number of silver stamps sold
= 40% x 5 u
=
40100 x 5 u
= 2 u
| |
Silver stamps |
Blue stamps |
Total |
| Number |
3 u |
2 u |
|
| Value |
$5 |
$10 |
|
| Total value |
15 u |
20 u |
$140 |
Total cost of unsold stamps
= 15 u + 20 u
= 35 u
35 u = 140
1 u = 140 ÷ 35 = 4
Number of blue stamps that Mary had left
= 20 u
= 20 x 4
= 80
Answer(s): 80
