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• ### $450 Tuition Credit & Official CAT Packs FREE January 15, 2019 January 15, 2019 10:00 PM PST 11:00 PM PST EMPOWERgmat is giving away the complete Official GMAT Exam Pack collection worth$100 with the 3 Month Pack ($299) • ### The winning strategy for a high GRE score January 17, 2019 January 17, 2019 08:00 AM PST 09:00 AM PST Learn the winning strategy for a high GRE score — what do people who reach a high score do differently? We're going to share insights, tips and strategies from data we've collected from over 50,000 students who used examPAL. # What is the probability of flipping a fair coin three times and the co  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics Author Message TAGS: ### Hide Tags Director Joined: 07 Jun 2004 Posts: 599 Location: PA What is the probability of flipping a fair coin three times and the co [#permalink] ### Show Tags Updated on: 29 Mar 2017, 20:32 00:00 Difficulty: 15% (low) Question Stats: 76% (00:52) correct 24% (00:58) wrong based on 94 sessions ### HideShow timer Statistics What is the probability of flipping a fair coin three times and the coin landing on heads on exactly two flips? A. 3/8 B. 5/8 C. 7/8 D. 1/8 E. 1/4 Originally posted by rxs0005 on 22 Dec 2010, 06:20. Last edited by Bunuel on 29 Mar 2017, 20:32, edited 1 time in total. Renamed the topic and edited the question. Math Expert Joined: 02 Sep 2009 Posts: 52108 Re: What is the probability of flipping a fair coin three times and the co [#permalink] ### Show Tags 22 Dec 2010, 06:25 rxs0005 wrote: What is the probability of flipping a fair coin three times and the coin landing on heads on exactly two flips? 3/8 5/8 7/8 1/8 1/4 $$P(H=2)=\frac{3!}{2!}*\frac{1}{2^3}=\frac{3}{8}$$, multiplying by 3!/2! as the case of 2 heads out of 3 tries can occur in 3 ways: HHT, HTH, THH - # of permutation of 3 letters out of which 2 are identical. Answer: A. _________________ Manager Joined: 25 Jul 2010 Posts: 145 Re: What is the probability of flipping a fair coin three times and the co [#permalink] ### Show Tags 02 Jan 2011, 02:10 1 Probability = (Favorable combination)/(Total combination) Favorable combination = (HHT, HTH, THH) ==> 3 Total combination = 8 (2^3) Probability = (3)/(8) (A) _________________ Raptor Target Test Prep Representative Status: Head GMAT Instructor Affiliations: Target Test Prep Joined: 04 Mar 2011 Posts: 2830 Re: What is the probability of flipping a fair coin three times and the co [#permalink] ### Show Tags 04 Apr 2017, 15:01 rxs0005 wrote: What is the probability of flipping a fair coin three times and the coin landing on heads on exactly two flips? A. 3/8 B. 5/8 C. 7/8 D. 1/8 E. 1/4 We can assume the first 2 flips are heads (H) and the last flip is tails (T). Thus: P(H-H-T) = 1/2 x 1/2 x 1/2 = 1/8 However, we need to determine in how many ways we can get 2 heads and 1 tails. That number will be equivalent to how many ways we can organize the letters H-H-T. We use the indistinguishable permutations formula to determine the number of ways to arrange H-H-T: 3!/2! = 3 ways. (Note: The 3 ways are H-H-T, H-T-H, and T-H-H.) Each of these 3 ways has the same probability of occurring. Thus, the total probability is: 1/8 x 3 = 3/8 Answer: A _________________ Jeffery Miller Head of GMAT Instruction GMAT Quant Self-Study Course 500+ lessons 3000+ practice problems 800+ HD solutions EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 13325 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: Q170 V170 Re: What is the probability of flipping a fair coin three times and the co [#permalink] ### Show Tags 05 Apr 2017, 19:19 1 Hi All, This question can be solved simply by listing out the possibilities and answering the exact question that is asked. Since we're flipping a coin 3 times, there are only (2)(2)(2) = 8 possible outcomes. They are... HHH HHT HTH THH TTT TTH THT HTT We're asked for the probability of getting exactly 2 HEADS from those 3 tosses. There are three ways (out of 8 total) to get exactly 2 heads (HHT, HTH and THH). Final Answer: GMAT assassins aren't born, they're made, Rich _________________ 760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com # Rich Cohen Co-Founder & GMAT Assassin Special Offer: Save$75 + GMAT Club Tests Free
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Re: What is the probability of flipping a fair coin three times and the co &nbs [#permalink] 05 Apr 2017, 19:19
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