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How many five-digit positive integers, divisible by 9, can be written using only the digits 3 and 6?

 Jun 10, 2020
 #1
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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. 

 Jun 10, 2020
 #2
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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.

MrToxicSharke  Jun 10, 2020
 #3
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then you should see how many ways you can order the nums. 

 Jun 10, 2020
 #4
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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

 Jun 10, 2020
 #5
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33336 , 33363 , 33633 , 36333 , 36666 , 63333 , 63666 , 66366 , 66636 , 66663 , Total =  10 such numbers

 Jun 10, 2020

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