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At least 3 zeroes (Posted on 2018-10-03) Difficulty: 3 of 5
How many binary strings of length n, having three or more zeroes, exist?

No Solution Yet Submitted by Ady TZIDON    
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solution | Comment 1 of 5
There are nC0=1 strings with exactly 0 zeroes.

There are nC1=n strings with exactly 1 zero.

There are nC2=n(n-1)/2 strings with exactly 2 zeroes.

There are 2^n total strings.

Thus the number of strings with 3 or more zeroes is

2^n-n(n-1)/2-n-1

  Posted by Daniel on 2018-10-03 07:48:06
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