Using the digits 7, 8, and 9 without repeating any digit, you can form:

  • 1-digit numbers: 3
  • 2-digit numbers: 6
  • 3-digit numbers: 6

So the total is 15 numbers.

Quick Scoop

For 1 digit, you have 3 choices: 7, 8, or 9. For 2 digits, you have 3×2=63\times 2=63×2=6 choices. For 3 digits, you have 3×2×1=63\times 2\times 1=63×2×1=6 choices.

Final Count

3+6+6=153+6+6=153+6+6=15

So the answer is 15.