Author 
Message 
TAGS:

Hide Tags

Current Student
Joined: 31 Aug 2007
Posts: 365

When tossed, a certain coin has equal probability of landing on either [#permalink]
Show Tags
Updated on: 28 Apr 2015, 04:07
3
This post received KUDOS
13
This post was BOOKMARKED
Question Stats:
51% (00:22) correct 49% (00:17) wrong based on 554 sessions
HideShow timer Statistics
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
Official Answer and Stats are available only to registered users. Register/ Login.
Originally posted by young_gun on 25 Dec 2007, 12:52.
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.



Director
Joined: 12 Jul 2007
Posts: 855

Re: When tossed, a certain coin has equal probability of landing on either [#permalink]
Show Tags
25 Dec 2007, 13:06
8
This post received KUDOS
3
This post was BOOKMARKED
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)



Manager
Joined: 06 Apr 2010
Posts: 135

When tossed, a certain coin has equal probability of landing [#permalink]
Show Tags
17 Aug 2010, 06:18
3
This post was BOOKMARKED
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



Math Expert
Joined: 02 Sep 2009
Posts: 44644

Re: Some PS questions Need explanation [#permalink]
Show Tags
17 Aug 2010, 07:24
5
This post received KUDOS
Expert's post
2
This post was BOOKMARKED



Manager
Joined: 21 Oct 2013
Posts: 191
Location: Germany
GPA: 3.51

Re: Some PS questions Need explanation [#permalink]
Show Tags
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. Answer: B. 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?



Math Expert
Joined: 02 Sep 2009
Posts: 44644

Re: Some PS questions Need explanation [#permalink]
Show Tags
13 Jan 2014, 07:22



Manager
Joined: 26 May 2013
Posts: 96

Re: When tossed, a certain coin has equal probability of landing on either [#permalink]
Show Tags
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 .



Manager
Joined: 20 Apr 2013
Posts: 150

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



Intern
Joined: 08 Sep 2014
Posts: 25
GMAT Date: 07112015
GPA: 2.9
WE: Account Management (Computer Software)

When tossed, a certain coin has equal probability of landing [#permalink]
Show Tags
20 May 2015, 16:40
Probability of landing on the same side every time: 1  (1/2 + 1/4) = 1/4



Manager
Joined: 13 Dec 2013
Posts: 164
Location: United States (NY)
Concentration: Nonprofit, International Business
GMAT 1: 710 Q46 V41 GMAT 2: 720 Q48 V40
GPA: 4
WE: Consulting (Consulting)

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



Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 2464
Location: United States (CA)

Re: When tossed, a certain coin has equal probability of landing [#permalink]
Show Tags
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 3toss outcome will be either HHH or TTT. P(TTT) = 1/2 x 1/2 x 1/2 = 1/8 P(HHH) = 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. Answer: B
_________________
Scott WoodburyStewart
Founder and CEO
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions



SVP
Joined: 12 Sep 2015
Posts: 2316
Location: Canada

Re: When tossed, a certain coin has equal probability of landing [#permalink]
Show Tags
13 Dec 2017, 14:32
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 P(3 matching tosses) = P(ANY result on 1st toss AND 2nd toss matches 1st toss AND 3rd toss matches 2nd toss) = P(ANY result on 1st toss) x P(2nd toss matches 1st toss ) x P(3rd toss matches 2nd toss) = 1 x 1/2 x 1/2 = 1/4 = B Cheers, Brent
_________________
Brent Hanneson – Founder of gmatprepnow.com



Intern
Joined: 22 Oct 2016
Posts: 3

Re: When tossed, a certain coin has equal probability of landing [#permalink]
Show Tags
28 Feb 2018, 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) Great explanation!!! Thank you!




Re: When tossed, a certain coin has equal probability of landing
[#permalink]
28 Feb 2018, 12:12






