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Hannibal lecter

Member

Registered: 2016-02-11

Posts: 392

how many permutation the following set has

Hi, how many permutation the set has X= ={1,1,2,2,6}

int  repetitions and without  repetitions

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Wisdom is a tree which grows in the heart and fruits on the tongue

Bob

Administrator

Registered: 2010-06-20

Posts: 10,640

Re: how many permutation the following set has

hi Hannibal lecter

If repetitions are allowed:

If the five numbers were all different it would be 5! = 5x4x3x2x1.

But we have repeated 1s.  You couldn't tell the difference between 16122 and 16122 where I have swapped the 1s around.  So very possibility gets counted twice because of the repeated 1s and similarly the 2s.  S we need to calculate 5! ÷ 2 ÷ 2

If repetitions are not allowed the set is effectively reduced to {1,2,6} so it's just 3! = 3x2x1.

126, 162, 261, 216, 612, 621.

Bob

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