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Probability Q

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Manager
Manager
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Joined: 02 Aug 2007
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Probability Q [#permalink] New post 15 Oct 2007, 11:32
Here's a probability question -

When tossed, a certain coin has the probability of landing on either side. If the coin is tossed 3 times, what is the probability that it will land on the same side each time?

A. 1/8
B. 1/4
C. 1/3
D. 3/8
E. 1/2

I chose A (1/2)(1/2)(1/2) = 1/8 (independent events) is this wrong?
Director
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Re: Probability Q [#permalink] New post 15 Oct 2007, 11:40
yuefei wrote:
Here's a probability question -

When tossed, a certain coin has the probability of landing on either side. If the coin is tossed 3 times, what is the probability that it will land on the same side each time?

A. 1/8
B. 1/4
C. 1/3
D. 3/8
E. 1/2

I chose A (1/2)(1/2)(1/2) = 1/8 (independent events) is this wrong?



I would choose 1/8, same reasoning...?
SVP
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 [#permalink] New post 15 Oct 2007, 12:00
It's (B) :)

There are 2 faces that are different... So either u consider the first tossing meaningless or u have to consider 3 times one side then 3 times the other side.

P = 1 * 1/2 * 1/2 = 1/4
or
P = P(Side1) + P(Side2) = 1/2 * 1/2 * 1/2 + 1/2 * 1/2 * 1/2 = 1/4
Director
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 [#permalink] New post 15 Oct 2007, 12:03
Fig wrote:
It's (B) :)

There are 2 faces that are different... So either u consider the first tossing meaningless or u have to consider 3 times one side then 3 times the other side.

P = 1 * 1/2 * 1/2 = 1/4
or
P = P(Side1) + P(Side2) = 1/2 * 1/2 * 1/2 + 1/2 * 1/2 * 1/2 = 1/4


Got it! nice one :)

when tossed for the first time the probability that it will land on either side is one.

thanks, Fig.
Director
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 [#permalink] New post 15 Oct 2007, 22:23
All heads Or All tails:
(3C3 + 3C0)* (1/2)^3 = 1/4
  [#permalink] 15 Oct 2007, 22:23
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