How many integers from 10 through 99 have distinct digits?
Solution using the Multiplication Rule:
[# of ints w/ dist. digits] = [# ways to pick digit 1] * [# ways to pick digit 2].
Since there are 9 ways to determine the 1st digit and (10 – 1 = 9) ways to determine the second digit,
[9] * [9] = 81
So there are 81 integers from 10-99 with distinct digits.
I'm not understanding the part where it says the "# of ways to pick digit 1 or 2". Are the numbers coming from the fact that the ones digit from 10 to 19 are 10 numbers total? But why 9? I've always been bad with numbers.. so apologies if this is common sense, but I really do not understand where these numbers came from (9*9 for example)
No comments:
Post a Comment