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PS-Probability

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Senior Manager
Joined: 05 Jun 2008
Posts: 304

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25 Nov 2008, 21:06
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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%

Pl help me to solve this,
Manager
Joined: 05 Jul 2008
Posts: 136
GMAT 2: 740 Q51 V38

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25 Nov 2008, 22:08
vivektripathi 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%

Pl help me to solve this,

My choice is B (not sure).
The number of interchanged names equals to the number of combinations that you take 2 out of the 5 letters to interchange. (5C2 = 10)
So there will be 10 combinations or 10 interchanged names.
There is only 1 combination (interchange 2 Es) the name is still the same.
=> The probability is 1/10= 10% (not sure)
Intern
Joined: 04 Jun 2008
Posts: 17

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25 Nov 2008, 23:09
10%

total interchanges possible = 5C2 = 10

no of interchanges in which name does not change = 1 (E interchanged with E)

so P= (1/10)*100 = 10%
Director
Joined: 14 Aug 2007
Posts: 726

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26 Nov 2008, 07:02
Agree with B

Other approach can be...total possible combinations = 20 (5*4*1*1*1)
The name remains same when EE is interchanged, 2 such combinations

2/20 = 10%
Re: PS-Probability   [#permalink] 26 Nov 2008, 07:02
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