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by eam 2656 days ago
Permutation without repetition.

The formula is:

n! / (n − r)!

Since there is 10 (n=10) total numbers, 0-9. And it can only be 3 (r=3) digits long. Then it would be,

10! / (10-3)!* which would result in,

10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1 / (7 * 6 * 5 * 4 * 3 * 2 * 1) = 10 * 9 * 8 = 720.