8 days ago, Nicole had a total of 225 red and black erasers. 20% of her erasers were black erasers. Today, her grandfather gave her some more erasers. As a result, her red erasers increased by 30%. Now, 50% of her erasers are black erasers. How many black erasers did her grandfather give her?
| |
Black erasers |
Red erasers |
Total
erasers |
| Before |
1 u |
4 u |
225 |
| Change |
+ 4.2 u |
+ 1.2 u |
|
| After |
5.2 u |
5.2 u |
|
Comparing the
red erasers and
black erasers in the end |
1 |
1 |
|
20% =
20100 =
15 Black erasers : Red erasers = 1 : 4
Increase in the number of red erasers
= 30% x 4 u
=
30100 x 4 u
= 1.2 u
50% =
50100 =
12 In the end
Black erasers : Red erasers = 1 : 1
Number of erasers at first
= 4 u + 1 u
= 5 u
5 u = 225
1 u = 225 ÷ 5 = 45
Number of black erasers that Nicole received from her grandfather
= 5.2 u - 1 u
= 4.2 u
= 4.2 x 45
= 189
Answer(s): 189
