Winnie had 20 pens.
25 were white and the rest were silver and red. The ratio of the number of silver pens to the number of red pens was 1 : 5. Winnie decided to buy some more white pens to increase the number of white pens to half of the total number of pens.
- How many less silver pens than white pens did he have at first?
- How many more white pens did he have to buy?
| White pens |
Silver pens |
Red pens |
Total |
| 2x2 |
3x2 |
|
| |
1x1 |
5x1 |
|
| 4 u |
1 u |
5 u |
20 |
| |
White pens |
Silver pens |
Red pens |
| Before |
4 u |
1 u |
5 u |
| Change |
+ ? |
|
|
| After |
6 u |
6 u |
Comparing white, silver
and red pens
in the end |
1 |
1 |
(a)
The total number of silver pens and red pens is repeated. Make the total number of silver pens and red pens the same. LCM of 3 and 6 is 6.
Total number of pens at first
= 4 u + 1 u + 5 u
= 10 u
10 u = 20
1 u = 20 ÷ 10 = 2
Number of less silver pens than white pens at first
= 4 u - 1 u
= 3 u
= 3 x 2
= 6
(b)
Number of more white pens that Winnie had to buy
= 6 u - 4 u
= 2 u
= 2 x 2
= 4
Answer(s): (a) 6; (b) 4
