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Probability [#permalink] New post 01 Apr 2006, 22:48
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 :)
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 [#permalink] New post 01 Apr 2006, 23:33
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
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 [#permalink] New post 02 Apr 2006, 00:28
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
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 [#permalink] New post 02 Apr 2006, 01:24
Yep.. Its C.

I like ur photo SimaQ
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 [#permalink] New post 02 Apr 2006, 01:33
sm176811 wrote:
Yep.. Its C.

I like ur photo SimaQ


I like it also :lol:
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 [#permalink] New post 02 Apr 2006, 19:26
yeap its C... i didnt know it was a combination problem... thats probably why i wasnt getting it.. thanks
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  [#permalink] 02 Apr 2006, 19:26
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