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Probability - unfair coin

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r2kins: Senior | Next Rank: 100 Posts; Posts: 58; Joined: Sat Apr 17, 2010 7:30 am; Thanked: 2 times

by r2kins » Thu May 12, 2011 2:10 am

The probability is 0.6 that an "unfair" coin will turn up tails on any given toss. If the coin is tossed 3 times, what is the probability that at least one of the tosses will turn up tails?

0.064
0.36
0.64
0.784
0.936

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Source: Beat The GMAT — Problem Solving | Thu May 12, 2011 2:10 am

manpsingh87: Master | Next Rank: 500 Posts; Posts: 436; Joined: Tue Feb 08, 2011 3:07 amFollowed by: 6 members; Thanked: 72 times

by manpsingh87 » Thu May 12, 2011 2:31 am

r2kins wrote:The probability is 0.6 that an "unfair" coin will turn up tails on any given toss. If the coin is tossed 3 times, what is the probability that at least one of the tosses will turn up tails?

0.064
0.36
0.64
0.784
0.936

probability that at least one of the tosses will turn up tails= 1- ( none will turn up tails)

{HHH} is the only case where none of the coin will turn up tails, also probability of occurrence of head= 0.4; hence required probability is 1-(0.4)*(0.4)*(0.4)= 1-.064=0.936 hence E

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8152; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

Re: Probability - unfair coin

by Scott@TargetTestPrep » Thu Jan 16, 2020 6:39 am

r2kins wrote: ↑
Thu May 12, 2011 2:10 am
The probability is 0.6 that an "unfair" coin will turn up tails on any given toss. If the coin is tossed 3 times, what is the probability that at least one of the tosses will turn up tails?

0.064
0.36
0.64
0.784
0.936

We can use the formula:

P(At least 1 tail) = 1 - P(no tails)

P(no tails) = 0.4 x 0.4 x 0.4 = 0.064

P(at least 1 tail) = 1 - 0.064 = 0.936

Answer: E

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