How many 3-digit numbers have no zeros? How many 3-digit numbers have no zeros and no fives? How many 3-digit numbers have no zeros but at least one five?
I'm just really confused on how to do this. I figured the first was 729 and the second was 512 but I'm very stuck on the third one.
On
Hints
1) How many 3-digits numbers at all ? How many of them have zeroes ? How can you get your answer using this information?
2)The same idea there are 900 3-digits numbers at all. How many numbers of them have $0$ or $5$ in representation?
3)First digit isn't $0$ assume that first one is $5$ , then how many numbers with no zero digits you have? The same idea if you have $5$ at second position , e.t.c. But don't forget about numbers you may count twice!
HINT
For the third case let start from case 1 and subtract the number of cases without 0 and 5.