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Founder  Joined: 18 Apr 2015
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A coin is tossed six times. What is the probability of getti [#permalink]
Expert's post 00:00

Question Stats: 54% (01:36) correct 45% (01:13) wrong based on 22 sessions
A coin is tossed six times. What is the probability of getting at least four heads on the tosses?

A. $$\frac{1}{64}$$

B. $$\frac{3}{32}$$

C. $$\frac{15}{64}$$

D. $$\frac{11}{32}$$

E. $$\frac{90}{64}$$
[Reveal] Spoiler: OA

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Re: A coin is tossed six times. What is the probability of getti [#permalink]
Some one please explain this? I think I took the wrong route Founder  Joined: 18 Apr 2015
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Re: A coin is tossed six times. What is the probability of getti [#permalink]
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Expert's post
The probability is = N. of desired outcomes/N. of possible outcomes.

Starting to calculate your denominator, we do have 6 tosses. Each one can give you Head or Tail : H or T.

For six times we do have $$2^6 = 64$$

Now, the denominator: at least four heads means 4 H, 5H or 6H.

To calculate 4 H we do use the combination formula $$6C2$$ (because we do have four H and 2 T) so we do have 15 possible combinations

$$6C5$$ we do have 6 combinations.

For $$6C6$$ actually is 1

$$15+6+1=22$$

Our probability is $$\frac{22}{64}= \frac{11}{32}$$ so the answer is D
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GRE Prep Club Members of the Month: Each member of the month will get three months free access of GRE Prep Club tests. Re: A coin is tossed six times. What is the probability of getti   [#permalink] 06 May 2018, 10:07
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