Spaced ones

MediumCombinatorics~5m

How many binary strings of length $10$ have exactly three $1$ 's, with no two of them adjacent?

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Lay out the $0$ 's first, then drop the $1$ 's into the gaps.
Non-adjacent choice: $\binom{n-k+1}{k}$ with $n=10$ , $k=3$ .

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