fozzzy wrote:
20 marbles were pulled out of a bag of only white marbles, painted black, and then put back in. Then, another 20 marbles were pulled out, of which 1 was black, afterwhich they were all returned to the bag. If the percentage of black marbles pulled out the second time represents their percentage in the bag, how many marbles in total does the bag currently hold?
A 40
B 200
C 380
D 400
E 3200
A 40
B 200
C 380
D 400
E 3200
From a bag of all white marbles, 20 become black.
The second time 1 black is pulled out, and \frac{1}{20}=5% represents the percentage of black marble in the bag.
We know that 5%=20 black , 20 is the number painted the first time (the ONLY black marble).
So there are a total of 20*20=400 marbles (20 black and 380 white).