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

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Manager
Joined: 11 Jan 2007
Posts: 193
Location: Bangkok
When tossed, a certain coin has equal probability of landing  [#permalink]

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Updated on: 27 Aug 2014, 04:20
1
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Difficulty:

25% (medium)

Question Stats:

56% (00:15) correct 44% (00:12) wrong based on 306 sessions

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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

OPEN DISCUSSION OF THIS QUESTION IS HERE: when-tossed-a-certain-coin-has-equal-probability-of-landing-99282.html

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cool

Originally posted by jet1445 on 28 Jul 2007, 09:53.
Last edited by Bunuel on 27 Aug 2014, 04:20, edited 1 time in total.
Renamed the topic, edited the question, added the OA and moved to PS forum.
Director
Joined: 08 Feb 2007
Posts: 600
Location: New Haven, CT
Re: When tossed, a certain coin has equal probability of landing  [#permalink]

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28 Jul 2007, 10:17
1/2 chance for one time. For 3 times it's (1/2)^3=1/8.
Senior Manager
Joined: 14 Jun 2007
Posts: 393
Re: When tossed, a certain coin has equal probability of landing  [#permalink]

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28 Jul 2007, 11:41
2
4
jet1445 wrote:
6. 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.1/2
D.2/3
E.5/8

I believe this was a trick question. They aren't asking for Pr 3 heads, or Pr 3 tails they are asking for Pr 3 heads or 3 tails = (Pr 3 H) + (Pr 3 T) - (Pr 3H and 3 T)
B:

Pr 3 tails = 1/8
Pr 3Hand3T=0

Pr 3 heads or 3 tails = 2/8 = 1/4
VP
Joined: 08 Jun 2005
Posts: 1136
Re: When tossed, a certain coin has equal probability of landing  [#permalink]

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28 Jul 2007, 11:48
1
anonymousegmat wrote:
jet1445 wrote:
6. 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.1/2
D.2/3
E.5/8

I believe this was a trick question. They aren't asking for Pr 3 heads, or Pr 3 tails they are asking for Pr 3 heads or 3 tails = (Pr 3 H) + (Pr 3 T) - (Pr 3H and 3 T)
B:

Pr 3 tails = 1/8
Pr 3Hand3T=0

Pr 3 heads or 3 tails = 2/8 = 1/4

I agree.

HHH = 1/8

TTT = 1/8

1/8+1/8 = 1/4

Good catch Anonymousegmat !

Manager
Joined: 11 Jul 2007
Posts: 57
Re: When tossed, a certain coin has equal probability of landing  [#permalink]

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19 Oct 2007, 07:41
2
1
I got the right answer: 1/4
But is my reasoning ok?

first toss determines the side (heads or tails). for the sake of this argument, i'll say HEADS.
=1 (probability is 1 cause it can go either way)
for the second & third toss, there's 1/2 probability that the toss will end up w/ HEADS
.....
1 * 1/2 * 1/2 = 1/4

i understand how other people solved it, but i was wondering if my method will apply to similar questions.
VP
Joined: 08 Jun 2005
Posts: 1136
Re: When tossed, a certain coin has equal probability of landing  [#permalink]

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19 Oct 2007, 07:54
prospective mba wrote:
I got the right answer: 1/4
But is my reasoning ok?

first toss determines the side (heads or tails). for the sake of this argument, i'll say HEADS.
=1 (probability is 1 cause it can go either way)
for the second & third toss, there's 1/2 probability that the toss will end up w/ HEADS
.....
1 * 1/2 * 1/2 = 1/4

i understand how other people solved it, but i was wondering if my method will apply to similar questions.

Yes I think your logic is solid

Manager
Joined: 11 Jul 2007
Posts: 57
Re: When tossed, a certain coin has equal probability of landing  [#permalink]

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19 Oct 2007, 07:58
thanks for the quick response!
i can see that your logic makes more sense, but my brain's just not wired to think that way.
Math Expert
Joined: 02 Sep 2009
Posts: 49431
Re: When tossed, a certain coin has equal probability of landing  [#permalink]

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27 Aug 2014, 04:20
jet1445 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.

OPEN DISCUSSION OF THIS QUESTION IS HERE: when-tossed-a-certain-coin-has-equal-probability-of-landing-99282.html
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Re: When tossed, a certain coin has equal probability of landing  [#permalink]

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13 Jul 2018, 04:01
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Re: When tossed, a certain coin has equal probability of landing &nbs [#permalink] 13 Jul 2018, 04:01
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