PSLE Billy had black pencils and purple pencils for sale. He sold 560 black pencils. 30% of the pencils sold were purple.
- How many black pencils and purple pencils did Billy sell altogether?
- He sold 50% of his pencils. 70% of the pencils left unsold were black. How many purple pencils did Billy have at first?
| |
Black |
Purple |
Total |
Total in percent |
| Before |
14 u |
6 u |
20 u |
100% |
| Change |
- 70%
- 7 u |
- 30%
- 3 u |
- 100%
- 10 u |
- 50% |
| After |
70%
7 u |
30%
3 u |
100%
10 u |
50%
|
30% =
30100 =
310 Total number of pencils sold = 10 u
Number of purple pencils sold = 3 u
Number of black pencils sold
= 10 u - 3 u
= 7 u
7 u = 560
1 u = 560 ÷ 7 = 80
Total number of pencils sold
= 10 u
= 10 x 80
= 800
(b)
Percent of the pencils left unsold = 100% - 50% = 50% 50% of the pencils that were sold = 10 u 50% of the pencils that were left unsold = 10 u Percent of the pencils left unsold that were black = 70%
Percent of the pencils left unsold that were purple = 100% - 70% = 30%
Number of the pencils left unsold that were purple
= 30% x 10 u
=
30100 x 10 u
= 3 u
Number of purple pencils that Billy had at first
= 3 u + 3 u
= 6 u
= 6 x 80
= 480
Answer(s): (a) 800; (b) 480
