Vanessa has a bag containing some black and green marbles. If she removes 7 black marbles, 30% of the marbles in the bag are green. If she adds another 28 green marbles, 50% of the marbles in the bag are green. How many black marbles are in the bag?
| |
Black marbles |
Green marbles |
| Before |
7 u + 7 |
3 u |
| Change 1 |
- 7 |
|
| After 1 |
7x1 =
7 u |
3x1 =
3 u |
| Change 2 |
|
+ 28 |
| After 2 |
1x7 =
7 u |
1x7 =
7 u |
30% =
30100 =
31050% =
50100 =
12The number of black marbles remains unchanged at the second change when she adds another 28 green marbles. Make the number of black marbles the same at the second change. LCM of 7 and 1 is 7.
Number of green marbles added
= 7 u - 3 u
= 4 u
4 u = 28
1 u = 28 ÷ 4 = 7
Number of black marbles at first
= 7 u + 7
= 7 x 7 + 7
= 49 + 7
= 56
Answer(s): 56
