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There are 20 red marbles, 20 blue marbles, 5 white marbles, [#permalink]
22 Jul 2008, 06:39

There are 20 red marbles, 20 blue marbles, 5 white marbles, and 5 green marbles in a bag. If two balls are to be selected at random, without replacement, what is the probability of getting two balls with the same color? A. 4/7 B. 19/25 C. 16/49 D. 32/49 E. 32/50

Re: probability, good one [#permalink]
22 Jul 2008, 06:43

arjtryarjtry wrote:

There are 20 red marbles, 20 blue marbles, 5 white marbles, and 5 green marbles in a bag. If two balls are to be selected at random, without replacement, what is the probability of getting two balls with the same color? A. 4/7 B. 19/25 C. 16/49 D. 32/49 E. 32/50

(C(20,2)+C(20,2)+C(5,2)+C(5,2))/C(50,2)=16/49 -> C

Re: probability, good one [#permalink]
22 Jul 2008, 06:44

16/49

i did

Chance to same color for each color = (\frac{20}{50}*\frac{19}{49})*2 + (\frac{5}{50}*\frac{4}{49})*2 (times 2 because there are 20 Red and 20 blue, so same numbers and same thing for White and Green with 5 each.

There are 20 red marbles, 20 blue marbles, 5 white marbles, and 5 green marbles in a bag. If two balls are to be selected at random, without replacement, what is the probability of getting two balls with the same color? A. 4/7 B. 19/25 C. 16/49 D. 32/49 E. 32/50

_________________

------------------------------------ J Allen Morris **I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

Re: probability, good one [#permalink]
22 Jul 2008, 06:49

arjtryarjtry wrote:

There are 20 red marbles, 20 blue marbles, 5 white marbles, and 5 green marbles in a bag. If two balls are to be selected at random, without replacement, what is the probability of getting two balls with the same color? A. 4/7 B. 19/25 C. 16/49 D. 32/49 E. 32/50

Re: probability, good one [#permalink]
22 Jul 2008, 06:52

Total numbers of possibilities (ordered): 50x49

Possibilities for 2 red marbles: 20x19 = 380 Possibilities for 2 blue marbles: 20x19 = 380 Possibilities for 2 white marbles: 5x4 = 20 Possibilities for 2 green marbles: 5x4 = 20

--> Total number of favorable possibilities = 800

Answer is 800/(50x49) = 16/49

==> Answer is (C)

gmatclubot

Re: probability, good one
[#permalink]
22 Jul 2008, 06:52