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As the title said, I have an assignment where we are asked: How many 2-digit numbers can be formed from even-numbered digits if the repetition of the digit is not allowed?

I've tried answering it myself but I am not sure if it's correct. What I did was multiply 4 by 3, since there are 4 even-numbered digits (2, 4, 6, 8). And since repetition is not allowed, for the ones digit, I did 4 since nothing has been used yet and for the tens digit I only used 3 since one digit has been used before. Please correct me if I'm wrong.

Sorry if my explanation is bad, I have a hard time trying to explain things and this is my first time posting. Many thanks!

Edit: Okay, just a quick update. I asked my teacher and apparently, both 12 and 16 are considered answers. Case closed! :)

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  • $\begingroup$ Welcome to MSE. You've overlooked the even digit $0$. $\endgroup$
    – saulspatz
    Apr 8, 2021 at 9:29

1 Answer 1

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What about the number $0$? While it can't be placed at the first digit, it can be placed at the second digit.

The first place has $4$ choices, after picking the first place, we have $4$ choices for the second place.

$4 \times 4 = 16$.

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  • $\begingroup$ I haven't thought about that since I'm not really sure if my teacher wants to include the number 0 in our problems. But that was great insight on this. Thanks a lot for the quick answer! $\endgroup$
    – mumu
    Apr 8, 2021 at 9:33

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