Olivia has a bag containing some red and black cards. If she removes 17 red cards, 20% of the cards in the bag are black. If she adds another 15 black cards, 50% of the cards in the bag are black. How many red cards are in the bag?
| |
Red cards |
Black cards |
| Before |
4 u + 17 |
1 u |
| Change 1 |
- 17 |
|
| After 1 |
4x1 =
4 u |
1x1 =
1 u |
| Change 2 |
|
+ 15 |
| After 2 |
1x4 =
4 u |
1x4 =
4 u |
20% =
20100 =
1550% =
50100 =
12The number of red cards remains unchanged at the second change when she adds another 15 black cards. Make the number of red cards the same at the second change. LCM of 4 and 1 is 4.
Number of black cards added
= 4 u - 1 u
= 3 u
3 u = 15
1 u = 15 ÷ 3 = 5
Number of red cards at first
= 4 u + 17
= 4 x 5 + 17
= 20 + 17
= 37
Answer(s): 37
