There are 648 integers between 100 and 1000 in which no digit is repeated.
Explanation
Let's break down why this is the case. We are looking for three-digit numbers (between 100 and 1000) where each digit is unique.
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Hundreds Digit: The first digit can be any number from 1 to 9. It cannot be 0 because then it wouldn't be a three-digit number. So, there are 9 possibilities.
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Tens Digit: Once we've chosen the first digit, we can now choose the second digit. It can be 0, but it cannot be the same as the first digit we chose. So, again, there are 9 possibilities.
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Units Digit: For the last digit, we cannot use either of the first two digits. This leaves us with 8 possibilities.
According to the reference, the total number of such integers is calculated by multiplying these possibilities together: 9 9 8 = 648.
