Is the following an unordered selection with or without repetition?

Question

The number of binary strings of length 100 that contain at most two 1s.

How do we write an expression for it?

score 1 · Accepted Answer · answered Apr 30 '16 at 14:51

1

${100\choose 2}+{100\choose 1} + {100\choose 0}$.

You have 100 digits, you choose 2/1/0 of them to be the 1's, the rest being zeroes.

answered Apr 30 '16 at 14:51

yoyostein

Thanks! Just want to clarify whether it's a permutation? – rainbow May 01 '16 at 05:23
Yes it is- in the sense that the order matters – yoyostein May 01 '16 at 07:42

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