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# Probability Q

Author Message
Manager
Joined: 02 Aug 2007
Posts: 145

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15 Oct 2007, 12:32
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

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
Joined: 22 Aug 2007
Posts: 566

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15 Oct 2007, 12:40
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
Joined: 01 May 2006
Posts: 1796

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15 Oct 2007, 13:00
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
Joined: 22 Aug 2007
Posts: 566

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15 Oct 2007, 13:03
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
Joined: 18 Jul 2006
Posts: 524

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15 Oct 2007, 23:23
(3C3 + 3C0)* (1/2)^3 = 1/4
15 Oct 2007, 23:23
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