Betty has a bag containing some silver and green cards. If she adds in 20 silver cards, 25% of the cards in the bag are green. If she adds in another 10 green cards, 30% of the cards in the bag are green. How many silver cards are in the bag?
| |
Silver cards |
Green cards |
| Before |
21 u - 20 |
7 u |
| Change 1 |
+ 20 |
|
| After 1 |
3x7 =
21 u |
1x7 =
7 u |
| Change 2 |
|
+ 10 |
| After 2 |
7x3 =
21 u |
3x3 =
9 u |
25% =
25100 =
1430% =
30100 =
310The number of silver cards remains unchanged at the second change when she adds in another 10 green cards. Make the number of silver cards the same at the second change. LCM of 3 and 7 is 21.
Number of green cards added
= 9 u - 7 u
= 2 u
2 u = 10
1 u = 10 ÷ 2 = 5
Number of silver cards at first
= 21 u - 20
= 21 x 5 - 20
= 105 - 20
= 85
Answer(s): 85
