Question

a 4 digit house number contains no zeros. the number has exactly three distinct digits. how many such numbers are there?

Answer 1

So there are 9 possible digits for the house number, 3 of which are unique. That means that for the first digit there are 9 combinations. For the second there are 8 (as it can't be the same as the first). For the third there are 7 (as it can't be the same as the first or second). For the fourth, there are 9 as only 3 digits are distinct.

Total number = 9*8*7*9 = 4536

Answer 2

okay, got it, thanks!

Answer 3

No problem!