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Easy probability question

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Director
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Easy probability question [#permalink] New post 06 Dec 2006, 06:24
Just wanted to see if many of you guys will fall for my "made up" trap :)

If the coin is tossed two times, what is the probability that it will turn up head at least once.

A) 1/4
B) 1/2
C) 1/6
D) 3/4
E) 1
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 [#permalink] New post 06 Dec 2006, 06:28
(D) for me :)

P(1 twist and no head) = 1/2

That implies,
P(2 twists and no head) = 1/2*1/2 = 1/4

Hence,
P(2 twists and at least 1 head) = 1 - 1/4= 3/4
Director
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 [#permalink] New post 06 Dec 2006, 06:48
But it has a little twist in it doesn't it? :)
Senior Manager
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 [#permalink] New post 06 Dec 2006, 06:53
1 - probability of 2 tails

1-(1/2*1/2) = 3/4

Last edited by MBAlad on 06 Dec 2006, 11:13, edited 1 time in total.
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 [#permalink] New post 06 Dec 2006, 09:00
Think in this way...
possible cases are HH, HT, TH and TT

so (HH and HT and TH) / (all cases) = 3/4
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 [#permalink] New post 06 Dec 2006, 11:31
anindyat wrote:
Think in this way...
possible cases are HH, HT, TH and TT

so (HH and HT and TH) / (all cases) = 3/4


good explaination
Director
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 [#permalink] New post 06 Dec 2006, 11:57
P atone head = 1 -P(none)
P(none)=1/2*1/2=1/4

therefore required =3/4
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 [#permalink] New post 06 Dec 2006, 11:59
You are all correct and avoided my trap, which was "at least once" :)
  [#permalink] 06 Dec 2006, 11:59
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