6 days ago, Eva had a total of 200 yellow and black cards. 25% of her cards were black cards. Today, her mother gave her some more cards. As a result, her yellow cards increased by 10%. Now, 50% of her cards are black cards. How many black cards did her mother give her?
| |
Black cards |
Yellow cards |
Total
cards |
| Before |
1 u |
3 u |
200 |
| Change |
+ 2.3 u |
+ 0.3 u |
|
| After |
3.3 u |
3.3 u |
|
Comparing the
yellow cards and
black cards in the end |
1 |
1 |
|
25% =
25100 =
14 Black cards : Yellow cards = 1 : 3
Increase in the number of yellow cards
= 10% x 3 u
=
10100 x 3 u
= 0.3 u
50% =
50100 =
12 In the end
Black cards : Yellow cards = 1 : 1
Number of cards at first
= 3 u + 1 u
= 4 u
4 u = 200
1 u = 200 ÷ 4 = 50
Number of black cards that Eva received from her mother
= 3.3 u - 1 u
= 2.3 u
= 2.3 x 50
= 115
Answer(s): 115
