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P and C

by nikhilagrawal » Wed Jul 23, 2008 4:22 am
My name is AJEET. But my son accidentally types the name by interchanging a pair of letters in my name. What is the probability that despite this interchange, the name remains unchanged?

a) 5%
b) 10%
c) 20%
d) 25%
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by sudhir3127 » Wed Jul 23, 2008 4:35 am
My answer is 10 %

2/20= 10%
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by reachac » Wed Jul 23, 2008 5:29 am
10%
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by nikhilagrawal » Wed Jul 23, 2008 5:53 am
can some one help me in determing the no of successful events.
I amy confused how we are getting 20 .. pls explain ..
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by acecoolan » Wed Jul 23, 2008 6:44 pm
Can someone explain this ....my Probability and Perm/Comb fundaes are totally 0 ..I think

Can anyone also suggest where to start afresh on these topics?
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Re: P and C

by Stuart@KaplanGMAT » Wed Jul 23, 2008 8:30 pm
nikhilagrawal wrote:My name is AJEET. But my son accidentally types the name by interchanging a pair of letters in my name. What is the probability that despite this interchange, the name remains unchanged?

a) 5%
b) 10%
c) 20%
d) 25%
There are 5C2 different pairs of letters in your name.

5C2 = 5!/2!3! = 5*4/2 = 10

So, there are 10 swaps that your son could make.

Only 1 of those swaps (E/E) would leave your name spelled correctly. So, there's a 1/10 chance that your name will still be fine: choose (b).

Just curious, why aren't there 5 answer choices?
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