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lyntam
Oct 13, 2008, 11:19 AM
If a box contains 4 red marbles, 7 white marbles, and 5 blue marbles. If one is drawn at random, what is the probability that both marbles are white if the draws are made without replacement?


Tammy Gilreath

ebaines
Oct 13, 2008, 12:13 PM
I assume you mean "if two are drawn at random," not one - correct?

You start with a total of 16 marbles, 7 of which are white. So on the first draw the probability of pulling a white marble is 7/16. If that is successful, then there are only 6 whites left out of the 15 remaining marbles, so the probability of pulling a second white marble is 6/15. Hence the probability of pulling two white marbles in a row without replacement is (7/16)*(6/15).