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Senior | Next Rank: 100 Posts
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by sumasajja » Thu Jul 21, 2011 1:56 pm
In a random selection of two people from a group of five-A, B, C, D, and E-what
is the probability of selecting A and B?

(A)
2/5

(B)
1/5

(C)
1/10

(D)
1/15

(E)
1/20

The correct answer is [spoiler]c

i thought the probability was 1/20 but it didn't match the answer ,,,can any1 explain me !!![/spoiler]
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by vineeshp » Thu Jul 21, 2011 6:47 pm
I guess you multiplied 1/5 * 1/4. That would have been right if the question said, probability of selecting B given A is already selected. Here 2 ppl are selected.

No of ways of selecting 2 ppl from 5 = 5C2 = 10
No of ways of selecting A and B = 1 (2C2)

Hence probability = 1/10.

PS: "explain me" is wrong language.
Vineesh,
Just telling you what I know and think. I am not the expert. :)
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by sumasajja » Thu Jul 21, 2011 9:28 pm
thanks.....for the explanation
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by kitg » Mon Jul 25, 2011 6:37 pm
hi.. i think probability =

(probability of choosing A and then choosing B) + (probability of choosing B then choosing A)
= (1/5 * 1/4) + (1/5 * 1/4) = 1/10
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