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# If you are flipping the coin 4 times, what is the probability of landi

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
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GMAT 1: 760 Q51 V42
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If you are flipping the coin 4 times, what is the probability of landi  [#permalink]

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04 Aug 2017, 02:26
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5% (low)

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91% (01:17) correct 9% (01:46) wrong based on 75 sessions

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If you are flipping the coin 4 times, what is the probability of landing on head two times?

A. $$\frac{3}{5}$$
B. $$\frac{4}{5}$$
C. $$\frac{3}{7}$$
D. $$\frac{4}{7}$$
E. $$\frac{3}{8}$$

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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
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"Only $149 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Director Joined: 04 Dec 2015 Posts: 750 Location: India Concentration: Technology, Strategy Schools: ISB '19, IIMA , IIMB, XLRI WE: Information Technology (Consulting) Re: If you are flipping the coin 4 times, what is the probability of landi [#permalink] ### Show Tags 04 Aug 2017, 03:07 1 2 MathRevolution wrote: If you are flipping the coin 4 times, what is the probability of landing on head two times? A. $$\frac{3}{5}$$ B. $$\frac{4}{5}$$ C. $$\frac{3}{7}$$ D. $$\frac{4}{7}$$ E. $$\frac{3}{8}$$ Coin is tossed $$4$$ times. P ($$2$$ heads) $$= (\frac{1}{2} * \frac{1}{2} * \frac{1}{2} * \frac{1}{2} )* 4C2$$ P ($$2$$ heads) $$= (\frac{1}{16}) * (\frac{4!}{2!2!})$$ P ($$2$$ heads) $$= (\frac{1}{16}) *(\frac{4 * 3 * 2!}{2 * 1 * 2!})$$ P ($$2$$ heads) $$= \frac{6}{16} = \frac{3}{8}$$ Answer (E)... _________________ Please Press "+1 Kudos" to appreciate. Manager Joined: 21 Jul 2017 Posts: 191 Location: India Concentration: Social Entrepreneurship, Leadership GMAT 1: 660 Q47 V34 GPA: 4 WE: Project Management (Education) If you are flipping the coin 4 times, what is the probability of landi [#permalink] ### Show Tags 04 Aug 2017, 04:41 1 MathRevolution wrote: If you are flipping the coin 4 times, what is the probability of landing on head two times? A. $$\frac{3}{5}$$ B. $$\frac{4}{5}$$ C. $$\frac{3}{7}$$ D. $$\frac{4}{7}$$ E. $$\frac{3}{8}$$ Two results for each of four coin flips. When ways to perform tasks in series, we multiply. So that is 2×2×2×2 results in total. That is 2[square]4 or 16. For the favourable case we need to count the ways to get 2 heads and 2 tails. The count of permutations of two pairs of symbols is: 4!/2!2!=6. This is easily confirmed by just counting. |HHTT,HTHT,HTTH,THHT,THTH,TTHH}=6 Thus the probability is: 6/16, or: 0.375 Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 7230 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: If you are flipping the coin 4 times, what is the probability of landi [#permalink] ### Show Tags 06 Aug 2017, 18:18 ==> Probability=Want/Total. Total=since the number of ways when throwing the coins each becomes head or tail 2 times, you get 2*2*2*2=16. Want=if it lands on head 2 times, it lands on tail 2 times, so you get 4!/2!2!=6. Thus, the probability=6/16=3/8. The answer is E. Answer: E _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$149 for 3 month Online Course"
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Re: If you are flipping the coin 4 times, what is the probability of landi   [#permalink] 06 Aug 2017, 18:18
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