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Probability

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by Thouraya » Sat Sep 17, 2011 12:51 am
A jar contains 3 red marbles and 2 blue marbles. If two marbles are selected at the same time, what is the probability that both marbles will be red?

How can I solve the above with the approach 1-Probability of None?

Thanks
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by knight247 » Sat Sep 17, 2011 1:31 am
3 Red 2 Blue

For solving using the complementary method

Probability that both are red+Aleast 1 is blue=1

For atleast one being blue we could have the following scenarios
BB BR RB
(1)BB=2/5*1/4=1/10
(2)BR=2/5*3/4=3/10
(3)RB=Same as #2 so 3/10

Adding all three scenarios we have 3/10+3/10+1/10=7/10

Subtracting this from 1 we have 1-7/10=3/10

Direct method
RR

3/5*2/4=3/10
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by aplavakarthik » Sat Sep 17, 2011 2:03 am
total marbles 5(3red+2blue)

selecting 2 from 5 is 5c2=10

for favorable now selecting 2 red from 3 is 3c2=3

probability =favorable/total=3/10
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