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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 solution | Comment 2 of 5 |
Altogether there are 2^n binary strings of length n. There is 1 that has no zeros, n that have one zero and C(n,2)=n*(n-1)/2 that have two zeros.

The answer is

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

  = 2^n - (n^2+n)/2 - 1

  Posted by Charlie on 2018-10-03 11:58:11
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