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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, 12:52
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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, 04:07, 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, 13:06
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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, 13:12
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, 06:18
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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, 07:24
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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, 07:01
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, 07:22
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, 05:42
Hello from the GMAT Club BumpBot!

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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, 20:03
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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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, 20:49
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, 22:49
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, 16:40
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, 08:11
Hello from the GMAT Club BumpBot!

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

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09 Apr 2017, 13:23
young_gun 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

1st throw: Probability of getting either side = 1
2nd throw: Probability of getting the first side = 1/2
3rd throw: Probability of getting the first side = 1/2

(1/2)*(1/2)=1/4

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Re: When tossed, a certain coin has equal probability of landing [#permalink]

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10 Apr 2017, 20:42
Bunuel wrote:
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.

Would 2 be the binomial coefficient? As in 2 * (1/8)?

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Re: When tossed, a certain coin has equal probability of landing [#permalink]

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18 Apr 2017, 16:44
young_gun 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

We need to determine the probability that a coin lands on the same side for all 3 tosses of the coin. This means that the 3-toss outcome will be either H-H-H or T-T-T.

P(T-T-T) = 1/2 x 1/2 x 1/2 = 1/8

P(H-H-H) = 1/2 x 1/2 x 1/2 = 1/8

Thus, the probability that the coin lands on the same side each time is 1/8 + 1/8 = 2/8 = 1/4.

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Re: When tossed, a certain coin has equal probability of landing   [#permalink] 18 Apr 2017, 16:44
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