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spoiled apple

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by shibal » Thu Jun 25, 2009 6:44 pm
A basket has 5 apples, one is spoiled. If Henry picked 2 apples simultaneously and at random, what is probability that the 2 selected apples will include the spoiled one.

oa [spoiler]2/5[/spoiler]
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Re: spoiled apple

by pops » Thu Jun 25, 2009 9:24 pm
shibal wrote:A basket has 5 apples, one is spoiled. If Henry picked 2 apples simultaneously and at random, what is probability that the 2 selected apples will include the spoiled one.

oa [spoiler]2/5[/spoiler]
Number of ways to select 2 apples: 5c2 = 10
Number of ways of selecting 2 apples with one spoiled=4c1 (since we have to select just one nice apple)
probability = 4c1/5c2 = 4/10 = 2/5
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Re: spoiled apple

by shibal » Sat Jun 27, 2009 12:09 pm
pops wrote: Number of ways of selecting 2 apples with one spoiled=4c1 (since we have to select just one nice apple)
i didn't get that part.... why 4c1?
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Re: spoiled apple

by Morgoth » Sat Jun 27, 2009 12:51 pm
shibal wrote:
pops wrote: Number of ways of selecting 2 apples with one spoiled=4c1 (since we have to select just one nice apple)
i didn't get that part.... why 4c1?
There are 5 apples, 4 good ones, 1 spoiled;

We have to find the probability of 1 good and 1 spoiled;

Therefore, total probability is

Select 1 good apple from 4 good apples 4C1 = 4

Select 1 bad apple from 1 spoiled = 1C1 = 1

Total combinations = 5C2 = 10

4*1 / 10 = 2/5.

Hope this helps.
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Re: spoiled apple

by dtweah » Sat Jun 27, 2009 1:47 pm
shibal wrote:A basket has 5 apples, one is spoiled. If Henry picked 2 apples simultaneously and at random, what is probability that the 2 selected apples will include the spoiled one.

oa [spoiler]2/5[/spoiler]
4 good apples 1 bad apples

First apple good second apple bad +First apple bad second apple good

4/5 x 1/4=1/5


1/5 X 4/4=1/5

1/5+1/5=2/5
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by shibal » Sat Jun 27, 2009 2:34 pm
dtweah, good job, much easier and faster...
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by ghacker » Sun Jun 28, 2009 6:52 am
We can look at the problem in this way

spoil : S good : G

S G1 G2 G3 G4

So there are 10 ways to take two apples , then S came be selected in 4 ways ( SG1 , SG2 ,SG3 ,SG4)

Answer is 4/10 = 2/5
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