Given: We have 10 numbers i.e. 0,1,2,3,4,5,6,7,8,9
To Find: Number of 3-digit numbers formed with no repetition of digits.
Conditions: No digit is repeated
Let us represent the 3-digit number
First place can be filled with 9 numbers, i.e. 1,2,3,4,5,6,7,8,9 (0 cannot be placed as it will make it a 2-digit number) = 9 ways
Second place can be filled with remaining 9 numbers (as one number is used already) = 9 ways
Similarly, third place can be filled with 8 numbers = 8 ways
Total number of 3-digit numbers which can be formed
= 9 × 9 × 8 = 648