The ratio of gold to grey stamps that Mary had was 5 : 3. The cost of each of the gold stamps was $3 and the cost of each of the grey stamps was $6. Mary sold 60% of the gold stamps and the total cost of the unsold stamps was $168. How many gold stamps did she have left?
| |
Gold stamps |
Grey stamps |
| Before |
5 u |
3 u |
| Change |
- 3 u |
|
| After |
2 u |
3 u |
Number of gold stamps sold
= 60% x 5 u
=
60100 x 5 u
= 3 u
| |
Gold stamps |
Grey stamps |
Total |
| Number |
2 u |
3 u |
|
| Value |
$3 |
$6 |
|
| Total value |
6 u |
18 u |
$168 |
Total cost of unsold stamps
= 6 u + 18 u
= 24 u
24 u = 168
1 u = 168 ÷ 24 = 7
Number of gold stamps that Mary had left
= 6 u
= 6 x 7
= 42
Answer(s): 42
