8 days ago, Kathy had a total of 300 black and blue marbles. 40% of her marbles were blue marbles. Today, her older brother gave her some more marbles. As a result, her black marbles increased by 25%. Now, 50% of her marbles are blue marbles. How many blue marbles did her older brother give her?
| |
Blue marbles |
Black marbles |
Total
marbles |
| Before |
2 u |
3 u |
300 |
| Change |
+ 1.75 u |
+ 0.75 u |
|
| After |
3.75 u |
3.75 u |
|
Comparing the
black marbles and
blue marbles in the end |
1 |
1 |
|
40% =
40100 =
25 Blue marbles : Black marbles = 2 : 3
Increase in the number of black marbles
= 25% x 3 u
=
25100 x 3 u
= 0.75 u
50% =
50100 =
12 In the end
Blue marbles : Black marbles = 1 : 1
Number of marbles at first
= 3 u + 2 u
= 5 u
5 u = 300
1 u = 300 ÷ 5 = 60
Number of blue marbles that Kathy received from her older brother
= 3.75 u - 2 u
= 1.75 u
= 1.75 x 60
= 105
Answer(s): 105
