How many sets of 3 numbers each can be formed from {1,2,...,20} if no two consecutive integers are to be used? I can't figure out how to count this... Can someone explain? Thanks.
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Originally Posted by jzellt How many sets of 3 numbers each can be formed from {1,2,...,20} if no two consecutive integers are to be used? How many ways can you arrange the string $\displaystyle 11100000000000000000$ so no two $\displaystyle 1's$ are together?
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