The ratio of red to brown stamps that Mary had was 5 : 2. The cost of each of the red stamps was $2 and the cost of each of the brown stamps was $7. Mary sold 20% of the red stamps and the total cost of the unsold stamps was $110. How many brown stamps did she have left?
| |
Red stamps |
Brown stamps |
| Before |
5 u |
2 u |
| Change |
- 1 u |
|
| After |
4 u |
2 u |
Number of red stamps sold
= 20% x 5 u
=
20100 x 5 u
= 1 u
| |
Red stamps |
Brown stamps |
Total |
| Number |
4 u |
2 u |
|
| Value |
$2 |
$7 |
|
| Total value |
8 u |
14 u |
$110 |
Total cost of unsold stamps
= 8 u + 14 u
= 22 u
22 u = 110
1 u = 110 ÷ 22 = 5
Number of brown stamps that Mary had left
= 14 u
= 14 x 5
= 70
Answer(s): 70
