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    Module 5 Day 2 Your Turn Part 3
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    • I
      InTeReStInG M5
      last edited by

      It says that "See the video for the explanation, but I have checked multiple times and I don't get why powers of ten have to do with the divisibility rule for 3 and 9. Can someone please help?
      Thanks!

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      • E
        energizedpanda M2★ M3★ M4 M5★ @InTeReStInG
        last edited by

        @neatlobster Try to see a pattern on what happens when you subtract 1 from powers of 10. You'll find something neat. ;D

        ~∑nergized Pand∆

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        • I
          InTeReStInG M5
          last edited by

          This post is deleted!
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          • I
            InTeReStInG M5 @energizedpanda
            last edited by

            @energizedpanda
            Hmm, We get 9, 99, 999, .... So they are all mutiples of nine. Ok, now what?
            P.S
            why isn't "9 is equal to 3^2" correct?

            debbieD 1 Reply Last reply Reply Quote 3
            • mathnerd_101M
              mathnerd_101 M0 M3
              last edited by mathnerd_101

              I haven't taken the course, but to prove the divisibility of 9 rule, basically what you do is write out the number in base ten form, or just like: a_110^n+a_210^(n-1)...+a_n10^0. So, we can take this modulo 9 and we get a_1+a_2...+a_n. So if a_1+a_2...+a_n is divisible by 9, then a_110^n+a_210^(n-1)...+a_n10^0 is divisible and our proof is complete.

              EDIT: The reason this has to do with powers of ten is because we write it out with powers of ten

              If you see the text messages between two programmers, here are some common acronyms to know:
              imo: iteration may overload
              brb: bad recursion brb
              rofl: right-oriented frame layout

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              • debbieD
                debbie ADMIN M0★ M1 M5 @InTeReStInG
                last edited by

                @neatlobster Please take a look at your other post where I answered your question. 🙂 https://forum.poshenloh.com/topic/707/question-what-does-it-mean-by-then-the-value-of-a-digit-in-its-place-is-exactly-the-sum-you-get-when-you-add-up-these-stray-1-s

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