# Math Help - How many sets?

1. ## How many sets?

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.

2. 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 $11100000000000000000$ so no two $1's$ are together?