jj 189

tyou · 发表于 2003-8-28 02:33:00

There are 500 marbles in a  jar, 200 are red, 100 are blue and 200 are green. if two marbles, one at a time without placements, are taken from the jar. what is the possibility that both marbles are red?

the answer:  C200,2/C500,2

It sounds to me that two marbles are taken out at one time from the jar, right?

what if to take one and then another one?  C200,1 *C199,1/C500,1*C499,1  -- that is what I thought. how do you think?

gt750 · 发表于 2003-8-28 02:46:00

Your understanding on jj is right.
If take one and then another without returning the previous to the orginal place, your method is right.

jj 189

jj 189

所属分类: GMAT考试

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