Question

How many 3-digit numbers can be formed by using the digits 1 to 9, if no digit is repeated?

Answer 1

Given $3$ digit numbers that can be formed using the digits from $1$ to $9$.
Required number of 3-digit numbers$=$ arranging $3$ digits with the total number of $9$ digits.
= ${}^9{P}_3=(9\times 8\times 7)=504.$
Hence, the required number of numbers $=504$.