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# Probability

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Manager
Joined: 21 Mar 2006
Posts: 131
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Kudos [?]: 4 [0], given: 0

Probability [#permalink]  01 Apr 2006, 21:48
Here's a nother example question.

If the probability of rain on any given day in City X is 50%, what is the probability that it rains on exactly 3 days in a 5-day period.

a. 8/125
b. 2/25
c. 5/16
d. 8/25
e. 3/4

I got the right answer by guessing but now i think i probably should learn it the right way
_________________

A.P.

GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5078
Location: Singapore
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Kudos [?]: 184 [0], given: 0

[#permalink]  01 Apr 2006, 22:33
There's a Binomial Distribution example in the Permutation, Combination and Probabilities sticky. Try reading it and see if you can solve this problem.

Example:
The probability of raining is 0.3 and not raining is 0.7. What is the probability of getting three days of rains among seven days?
C(7, 3)*0.3^3*0.7^4
Director
Joined: 05 Feb 2006
Posts: 902
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Kudos [?]: 51 [0], given: 0

[#permalink]  01 Apr 2006, 23:28
Answer C...

Total number of possibilities = 32..... 2*2*2*2*2 (five days, each day has an equal chance to be a rain day or dry day)

Favourable outcomes = 10 (number of ways to pick 3 rain days out of 5 in any order... 5C3)

Total probability = 10/32.... 5/16
VP
Joined: 29 Apr 2003
Posts: 1405
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[#permalink]  02 Apr 2006, 00:24
Yep.. Its C.

I like ur photo SimaQ
Director
Joined: 05 Feb 2006
Posts: 902
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[#permalink]  02 Apr 2006, 00:33
sm176811 wrote:
Yep.. Its C.

I like ur photo SimaQ

I like it also
Manager
Joined: 21 Mar 2006
Posts: 131
Followers: 1

Kudos [?]: 4 [0], given: 0

[#permalink]  02 Apr 2006, 18:26
yeap its C... i didnt know it was a combination problem... thats probably why i wasnt getting it.. thanks
_________________

A.P.

[#permalink] 02 Apr 2006, 18:26
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# Probability

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