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Probability Galore

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Probability Galore

by dtweah » Sat May 09, 2009 8:57 am
If a man tosses a coin until he obtains either 3 heads or 3 tails, what is the probability he will need 5 tosses?

(a) 1/4
(b) 3/8
(c) 5/8
(d) 7/16
(e) 11/32
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by scoobydooby » Sat May 09, 2009 9:10 am
the man will need 5 tosses when he has 2 heads or two tails in the first 4 tosses. probability of 2 heads/2 tails in the 4 tosses: 4C2/2^4
=6/16=3/8
hence, B

(took a cue from your solution of the probability question on baseball match :))
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by dtweah » Sat May 09, 2009 9:22 am
scoobydooby wrote:the man will need 5 tosses when he has 2 heads or two tails in the first 4 tosses. probability of 2 heads/2 tails in the 4 tosses: 4C2/2^4
=6/16=3/8
hence, B

(took a cue from your solution of the probability question on baseball match :))
You get it buddy. Several of these problems are related. I mean there is only so much spin you can put on a probability or a triangle question. This forum is beautiful.
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by scoobydooby » Sat May 09, 2009 9:28 am
thanks for posting them dtweah, whats the source? the questions are thought provoking :)
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by dtweah » Sat May 09, 2009 10:07 am
scoobydooby wrote:thanks for posting them dtweah, whats the source? the questions are thought provoking :)
I am getting them from David Essner and University of Maryland high school Math competitions. I just discovered that their questions approximate the difficulty level of GMAT especially for David Essner, (Just Google these) Some of Maryland's may be too stronger but the questions put you in gear for the tough GMAT Stuff. Anybody who practices these questions spanning several years will be in more than in good shape for the GMAT or GRE.
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