How many five-digit positive integers, divisible by 9, can be written using only the digits 3 and 6?
+25 Well, to start, first go over the divisibility rule of 9: add up all digits and if the sum is divisible by nine, then the number is divisible by nine.
+25 then you should see how many ways you can add up to 9, 18, and 27 using only the addends of 6 and 3, and only 5 addends.
+25 for ex: 3+3+3+6+3
four 3s and only one 6.
you can arrange four 3s and one 6 five ways:
63333
36333
33633
33363
33336
