PSLE Tom had black notebooks and blue notebooks for sale. He sold 80 black notebooks. 60% of the notebooks sold were blue.
- How many black notebooks and blue notebooks did Tom sell altogether?
- He sold 50% of his notebooks. 80% of the notebooks left unsold were black. How many blue notebooks did Tom have at first?
| |
Black |
Blue |
Total |
Total in percent |
| Before |
6 u |
4 u |
10 u |
100% |
| Change |
- 40%
- 2 u |
- 60%
- 3 u |
- 100%
- 5 u |
- 50% |
| After |
80%
4 u |
20%
1 u |
100%
5 u |
50%
|
60% =
60100 =
35 Total number of notebooks sold = 5 u
Number of blue notebooks sold = 3 u
Number of black notebooks sold
= 5 u - 3 u
= 2 u
2 u = 80
1 u = 80 ÷ 2 = 40
Total number of notebooks sold
= 5 u
= 5 x 40
= 200
(b)
Percent of the notebooks left unsold = 100% - 50% = 50% 50% of the notebooks that were sold = 5 u 50% of the notebooks that were left unsold = 5 u Percent of the notebooks left unsold that were black = 80%
Percent of the notebooks left unsold that were blue = 100% - 80% = 20%
Number of the notebooks left unsold that were blue
= 20% x 5 u
=
20100 x 5 u
= 1 u
Number of blue notebooks that Tom had at first
= 1 u + 3 u
= 4 u
= 4 x 40
= 160
Answer(s): (a) 200; (b) 160
