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 wo

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.