PSLE Owen had red pens and black pens for sale. He sold 120 red pens. 70% of the pens sold were black.
- How many red pens and black pens did Owen sell altogether?
- He sold 50% of his pens. 60% of the pens left unsold were red. How many black pens did Owen have at first?
| |
Red |
Black |
Total |
Total in percent |
| Before |
9 u |
11 u |
20 u |
100% |
| Change |
- 30%
- 3 u |
- 70%
- 7 u |
- 100%
- 10 u |
- 50% |
| After |
60%
6 u |
40%
4 u |
100%
10 u |
50%
|
70% =
70100 =
710 Total number of pens sold = 10 u
Number of black pens sold = 7 u
Number of red pens sold
= 10 u - 7 u
= 3 u
3 u = 120
1 u = 120 ÷ 3 = 40
Total number of pens sold
= 10 u
= 10 x 40
= 400
(b)
Percent of the pens left unsold = 100% - 50% = 50% 50% of the pens that were sold = 10 u 50% of the pens that were left unsold = 10 u Percent of the pens left unsold that were red = 60%
Percent of the pens left unsold that were black = 100% - 60% = 40%
Number of the pens left unsold that were black
= 40% x 10 u
=
40100 x 10 u
= 4 u
Number of black pens that Owen had at first
= 4 u + 7 u
= 11 u
= 11 x 40
= 440
Answer(s): (a) 400; (b) 440
