Rachel has a bag containing some gold and black cards. If she removes 7 gold cards, 20% of the cards in the bag are black. If she removes another 20 black cards, 10% of the cards in the bag are black. How many gold cards are in the bag?
| |
Gold cards |
Black cards |
| Before |
36 u + 7 |
9 u |
| Change 1 |
- 7 |
|
| After 1 |
4x9 =
36 u |
1x9 =
9 u |
| Change 2 |
|
- 20 |
| After 2 |
9x4 =
36 u |
1x4 =
4 u |
20% =
20100 =
1510% =
10100 =
110The number of gold cards remains unchanged at the second change when she removes another 20 black cards. Make the number of gold cards the same at the second change. LCM of 4 and 9 is 36.
Number of black cards removed
= 9 u - 4 u
= 5 u
5 u = 20
1 u = 20 ÷ 5 = 4
Number of gold cards at first
= 36 u + 7
= 36 x 4 + 7
= 144 + 7
= 151
Answer(s): 151
