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# Easy probability question

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Director
Joined: 06 Feb 2006
Posts: 893

Kudos [?]: 129 [0], given: 0

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06 Dec 2006, 07:24
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

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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SVP
Joined: 01 May 2006
Posts: 1794

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06 Dec 2006, 07:28
(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

Kudos [?]: 169 [0], given: 0

Director
Joined: 06 Feb 2006
Posts: 893

Kudos [?]: 129 [0], given: 0

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06 Dec 2006, 07:48
But it has a little twist in it doesn't it?

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Senior Manager
Joined: 20 Feb 2006
Posts: 373

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06 Dec 2006, 07:53
1 - probability of 2 tails

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

Last edited by MBAlad on 06 Dec 2006, 12:13, edited 1 time in total.

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Senior Manager
Joined: 08 Jun 2006
Posts: 335

Kudos [?]: 63 [0], given: 0

Location: Washington DC

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06 Dec 2006, 10:00
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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Senior Manager
Joined: 17 Oct 2006
Posts: 432

Kudos [?]: 31 [0], given: 0

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06 Dec 2006, 12:31
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

Kudos [?]: 31 [0], given: 0

Senior Manager
Joined: 01 Oct 2006
Posts: 493

Kudos [?]: 41 [0], given: 0

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06 Dec 2006, 12:57
P atone head = 1 -P(none)
P(none)=1/2*1/2=1/4

therefore required =3/4

Kudos [?]: 41 [0], given: 0

Director
Joined: 06 Feb 2006
Posts: 893

Kudos [?]: 129 [0], given: 0

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06 Dec 2006, 12:59
You are all correct and avoided my trap, which was "at least once"

Kudos [?]: 129 [0], given: 0

06 Dec 2006, 12:59
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# Easy probability question

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