Probability Question

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ruchisharma: Junior | Next Rank: 30 Posts; Posts: 15; Joined: Sun Jun 13, 2010 8:15 pm

by ruchisharma » Fri Aug 13, 2010 6:57 am

When tossed, a certain coin has equal probability of landing on either side. If the coin is tossed 3
times, what is the probability that it will land on the same side each time?

A. 1/8 B. Â¼ C. 1/3 D. 3/8 E. Â½

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Source: Beat The GMAT — Problem Solving | Fri Aug 13, 2010 6:57 am

kmittal82: Master | Next Rank: 500 Posts; Posts: 324; Joined: Mon Jul 05, 2010 6:44 amFollowed by: 3 members; Location: London; Thanked: 70 times

by kmittal82 » Fri Aug 13, 2010 7:02 am

The question is simply asking whats the probability of having either 3 heads or 3 tails in 3 coin tosses:

P(3 heads) = 1/2 x 1/2 x 1/2 = 1/8

P(3 tails) = 1/2 x 1/2 x 1/2 = 1/8

P(3 heads or 3 tails) = p(3 heads) + p(3 tails) = 1/8 + 1/8 = 2/8 = 1/4

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