2026-04-24

Problem — 2026-04-24

Easy

Easycombinatorics

How many $4$ -digit numbers (from $1000$ to $9999$ ) have all digits distinct?

Enter an integer

Show solution

The first digit has

9

choices (

1

–

9

). The second digit has

9

choices (

0

–

9

minus the first). The third has

8

, the fourth has

7

. Total:

9 \times 9 \times 8 \times 7 = 4536