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# GMATprep practice question:probability coin

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GMATprep practice question:probability coin [#permalink]  07 Apr 2009, 10:33
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Question Stats:

20% (00:00) correct 80% (00:22) wrong based on 1 sessions
For one toss of a certain coin, the probability that the outcome is heads is 0.6. If this coin is tossed 5 times, which of the following is the probability that the outcome will be heads at least 4 times?
o (0.6)^5
o 2(0.6)^4
o 3(0.6)^4(0.4)
o 4(0.6)^4(0.4) + (O.6)^5
o 5(0.6)^4(Q.4) + (O.6)^5
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Re: GMATprep practice question:probability coin [#permalink]  07 Apr 2009, 12:10
pmal04 wrote:
For one toss of a certain coin, the probability that the outcome is heads is 0.6. If this coin is tossed 5 times, which of the following is the probability that the outcome will be heads at least 4 times?
o (0.6)^5
o 2(0.6)^4
o 3(0.6)^4(0.4)
o 4(0.6)^4(0.4) + (O.6)^5
o 5(0.6)^4(Q.4) + (O.6)^5

prob (4H1T)+prob (5H)=
5*0.6^4+0.6^5
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Re: GMATprep practice question:probability coin [#permalink]  13 Apr 2009, 06:22
It is E

Cases where head comes up four times:

H H H H T
H H H T H
H H T H H
H T H H H
T H H H H

5 x 0.6^4 x 0.4^1

Case where head comes up 5 times:

H H H H H

0.6^5

Together:

(5 x 0.6^4 x 0.4^1) + (0.6^5)
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Re: GMATprep practice question:probability coin [#permalink]  16 Apr 2009, 21:29
5(0.6)^4(Q.4) + (O.6)^5
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Re: GMATprep practice question:probability coin [#permalink]  17 Apr 2009, 03:48
best way to do it is to write it out (the possible solutions), - will take 30 s

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-talent is the desire to practice-

Re: GMATprep practice question:probability coin   [#permalink] 17 Apr 2009, 03:48
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