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Bunuel
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Lodz697

CrackverbalGMAT
Probability = Favorable Outcomes / Total Outcomes

There are 10 digits to be arranged. These have 5 even numbers.

Favorable Outcomes = Taking all even numbers as 1 unit.

External arrangement = Arranging 5 odd numbers + 1 unit of even numbers = (6 - 1)! = 5!

Internal arrangement = 5! (for all the even numbers)

Total favorable Outcomes = 5! * 5!


Total Arrangements = (10 - 1)! = 9!


The required probability = 5! * 5! / 9! = (5 * 4 * 3 * 2 * 5!) / ( 9 * 8 * 7 * 6 * 5!) = 5 / 126


Option C

Arun Kumar
­
Why are the total arrangements (10 -1)! ?

I took as total arrangements just 10! ...
­
  • The arrangement of n distinct objects in a row is denoted by n!.
  • The arrangement of n distinct objects in a circle is represented by (n-1)!.

The distinction between arranging in a row and in a circle is as follows: if we shift all objects by one position, we achieve a different arrangement in a row, but maintain the same relative arrangement in a circle. Therefore, for the number of circular arrangements of n objects, we have:

  • \(\frac{n!}{n} = (n-1)!\).

Check other Seating Arrangements in a Row and around a Table Questions.

Hope it helps.­
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Many thanks Bunuel
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How are there 5 even numbers ? I cn see nly 4 ... 2,4,6,8

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How are there 5 even numbers ? I cn see nly 4 ... 2,4,6,8

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Zero is an even number!!
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