The ratio of black to yellow stamps that Nora had was 5 : 3. The cost of each of the black stamps was $3 and the cost of each of the yellow stamps was $5. Nora sold 20% of the black stamps and the total cost of the unsold stamps was $135. How many yellow stamps did she have left?
|
Black stamps |
Yellow stamps |
Before |
5 u |
3 u |
Change |
- 1 u |
|
After |
4 u |
3 u |
Number of black stamps sold
= 20% x 5 u
=
20100 x 5 u
= 1 u
|
Black stamps |
Yellow stamps |
Total |
Number |
4 u |
3 u |
|
Value |
$3 |
$5 |
|
Total value |
12 u |
15 u |
$135 |
Total cost of unsold stamps
= 12 u + 15 u
= 27 u
27 u = 135
1 u = 135 ÷ 27 = 5
Number of yellow stamps that Nora had left
= 15 u
= 15 x 5
= 75
Answer(s): 75