11 days ago, Gillian had a total of 275 brown and black pens. 40% of her pens were black pens. Today, her mother gave her some more pens. As a result, her brown pens increased by 20%. Now, 50% of her pens are black pens. How many black pens did her mother give her?
| |
Black pens |
Brown pens |
Total
pens |
| Before |
2 u |
3 u |
275 |
| Change |
+ 1.6 u |
+ 0.6 u |
|
| After |
3.6 u |
3.6 u |
|
Comparing the
brown pens and
black pens in the end |
1 |
1 |
|
40% =
40100 =
25 Black pens : Brown pens = 2 : 3
Increase in the number of brown pens
= 20% x 3 u
=
20100 x 3 u
= 0.6 u
50% =
50100 =
12 In the end
Black pens : Brown pens = 1 : 1
Number of pens at first
= 3 u + 2 u
= 5 u
5 u = 275
1 u = 275 ÷ 5 = 55
Number of black pens that Gillian received from her mother
= 3.6 u - 2 u
= 1.6 u
= 1.6 x 55
= 88
Answer(s): 88
