The ratio of gold to black stamps that Yoko had was 5 : 3. The cost of each of the gold stamps was $1 and the cost of each of the black stamps was $5. Yoko sold 60% of the gold stamps and the total cost of the unsold stamps was $204. How many black stamps did she have left?
| |
Gold stamps |
Black 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 |
Black stamps |
Total |
| Number |
2 u |
3 u |
|
| Value |
$1 |
$5 |
|
| Total value |
2 u |
15 u |
$204 |
Total cost of unsold stamps
= 2 u + 15 u
= 17 u
17 u = 204
1 u = 204 ÷ 17 = 12
Number of black stamps that Yoko had left
= 15 u
= 15 x 12
= 180
Answer(s): 180
