When tossed, a certain coin has equal probability of landing : GMAT Problem Solving (PS)
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# When tossed, a certain coin has equal probability of landing

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When tossed, a certain coin has equal probability of landing on either [#permalink]

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25 Dec 2007, 11:52
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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
[Reveal] Spoiler: OA

Last edited by Bunuel on 28 Apr 2015, 03:07, edited 3 times in total.
Renamed the topic, edited the question and added the OA.
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Re: When tossed, a certain coin has equal probability of landing on either [#permalink]

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25 Dec 2007, 12:06
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There are 8 possibilities for outcomes when flipping a fair coin 3 times.

2*2*2=2^3=8

of these 8 possibilities there are 2 with the coin landing on the same side each time. HHH and TTT.

so the probability is 2/8 or 1/4.

HHH -- works
HHT
HTH
HTT
THH
THT
TTH
TTT -- works

the standard .5*.5*.5=1/8 but that's just the probability of getting one SPECIFIC side 3 times in a row (ie probability of 3 heads). Since they don't care if it's 3 heads or 3 tails you have to multiply 1/8 by 2 (so now it's the probability of 3 heads OR 3 tails)
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Re: When tossed, a certain coin has equal probability of landing on either [#permalink]

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25 Dec 2007, 12:12
eschn3am wrote:
There are 8 possibilities for outcomes when flipping a fair coin 3 times.

2*2*2=2^3=8

of these 8 possibilities there are 2 with the coin landing on the same side each time. HHH and TTT.

so the probability is 2/8 or 1/4.

HHH -- works
HHT
HTH
HTT
THH
THT
TTH
TTT -- works

the standard .5*.5*.5=1/8 but that's just the probability of getting one SPECIFIC side 3 times in a row (ie probability of 3 heads). Since they don't care if it's 3 heads or 3 tails you have to multiply 1/8 by 2 (so now it's the probability of 3 heads OR 3 tails)

thanks, i get that...just am not sure why the binomial distrib doesn't work for this problem...
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When tossed, a certain coin has equal probability of landing [#permalink]

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17 Aug 2010, 05:18
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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
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Re: Some PS questions- Need explanation [#permalink]

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17 Aug 2010, 06:24
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udaymathapati 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

Winning scenario is if we'll have either three tails (TTT) or three heads (HHH): 1/2*1/2*1/2+1/2*1/2*1/2=1/4.

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Re: Some PS questions- Need explanation [#permalink]

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13 Jan 2014, 06:01
Bunuel wrote:
udaymathapati wrote:
Need help in explanation of following problems. Need to know how quickly we can solve such problems to save time.

4. 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 E

Winning scenario is if we'll have either three tails (TTT) or three heads (HHH): 1/2*1/2*1/2+1/2*1/2*1/2=1/4.

Hi Bunuel,

if the question was "how high is the probability that you get only tails?" would it be answer B becaus 1/2*1/2*1/2 = 1/8?
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Re: Some PS questions- Need explanation [#permalink]

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13 Jan 2014, 06:22
unceldolan wrote:
Bunuel wrote:
udaymathapati wrote:
Need help in explanation of following problems. Need to know how quickly we can solve such problems to save time.

4. 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 E

Winning scenario is if we'll have either three tails (TTT) or three heads (HHH): 1/2*1/2*1/2+1/2*1/2*1/2=1/4.

Hi Bunuel,

if the question was "how high is the probability that you get only tails?" would it be answer B becaus 1/2*1/2*1/2 = 1/8?

Yes, P(TTT) = 1/2^3 = 1/8.
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Re: When tossed, a certain coin has equal probability of landing [#permalink]

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13 Feb 2015, 04:42
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Re: When tossed, a certain coin has equal probability of landing on either [#permalink]

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27 Apr 2015, 19:03
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Re: When tossed, a certain coin has equal probability of landing on either [#permalink]

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27 Apr 2015, 19:49
young_gun wrote:
eschn3am wrote:
There are 8 possibilities for outcomes when flipping a fair coin 3 times.

2*2*2=2^3=8

of these 8 possibilities there are 2 with the coin landing on the same side each time. HHH and TTT.

so the probability is 2/8 or 1/4.

HHH -- works
HHT
HTH
HTT
THH
THT
TTH
TTT -- works

the standard .5*.5*.5=1/8 but that's just the probability of getting one SPECIFIC side 3 times in a row (ie probability of 3 heads). Since they don't care if it's 3 heads or 3 tails you have to multiply 1/8 by 2 (so now it's the probability of 3 heads OR 3 tails)

thanks, i get that...just am not sure why the binomial distrib doesn't work for this problem...

Complements of the GMAT Club Bot, I will attempt to answer your questions 8 years later.

Binomial distribution doesn't work here because you must take into account the probability of HHH or TTT. = 1/8 + 1/8 = 2/8 = 1/4

This means you will add the two probabilities. You're likely confusing this question with something along the lines of "If I flip a coin 3 times, what is the probability of getting all heads" = 1/8 .
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Re: When tossed, a certain coin has equal probability of landing on either [#permalink]

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27 Apr 2015, 21:49
HHH or TTT = (1/2 * 1/2 * 1/2) + (1/2 * 1/2 * 1/2) = 1/8 + 1/8 = 1/4
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When tossed, a certain coin has equal probability of landing [#permalink]

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20 May 2015, 15:40
Probability of landing on the same side every time:
1 - (1/2 + 1/4) = 1/4
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Re: When tossed, a certain coin has equal probability of landing [#permalink]

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25 May 2016, 07:11
Hello from the GMAT Club BumpBot!

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Re: When tossed, a certain coin has equal probability of landing   [#permalink] 25 May 2016, 07:11
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