How many possible three-digit passwords can be formed using digits 0 through 9 if no digits are repeated?

The first digit can be 0 through 9, ten possibilities.

Having selected the first digit, you have 9 digits to pick from the second digit.

Having selected the second digit, you have 8 digits to pick from the third digit.

Hence total possibilities = 10 x 9 x 8 = 720