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coin-Probability

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by gmat740 » Tue Jul 28, 2009 3:15 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. 1/4
C. 1/3
D. 3/8
E. 1/2

OA-B

IMO=>Let coin lands on head side
so, P(head) = 1/2
3 times tossed= (1/2)*(1/2)*(1/2) =1/8

But this is not the answer.

Please correct me.
Last edited by gmat740 on Tue Jul 28, 2009 4:39 am, edited 1 time in total.
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by scoobydooby » Tue Jul 28, 2009 3:44 am
would go for B

there are two possibilites:

HHH or TTT

probability of HHH+probability of TTT=1/8+1/8=1/4
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by viju9162 » Tue Jul 28, 2009 7:39 am
I also got 1/8.. I always miss out what scoobydooby has mentioned.. there are equal chances for both head and tail to occur..

hence 1/8 + 1/8 = 1/4 ..

Thanks for posting the question
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Re: coin-Probability

by ankitns » Wed Jul 29, 2009 7:23 pm
The key here is to realize that we DONT care for 3 tosses...but only 2 tosses. It does not matter what the first toss is...but the second and third need to match it....

so say if the first was heads...probability of second to be heads is 1/2 and third to be head is also 1/2....hence 1/2*1/2 = 1/4.

Cheers.
gmat740 wrote: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. 1/4
C. 1/3
D. 3/8
E. 1/2

OA-B

IMO=>Let coin lands on head side
so, P(head) = 1/2
3 times tossed= (1/2)*(1/2)*(1/2) =1/8

But this is not the answer.

Please correct me.
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by shibal » Thu Jul 30, 2009 9:24 am
Basically it can land head or tail, it asks the prob of landing equally in the 3 attempts, hence it can be 3 times haed or tail

1/8 + 1/8 = 1/4
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