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54 mod 4

Module 5 Day 1 Challenge Part 7
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  • B
    Bella M0 M1 M2 M3 M4 M5
    last edited by Bella Apr 12, 2022, 6:15 AM Apr 12, 2022, 6:14 AM

    Professor Loh told us 27 + 27 (mod 4) = 3 + 3, which equals 6. The calculator says 27 + 27 (mod 4) = 2. Why?

    P 1 Reply Last reply Apr 20, 2022, 8:43 PM Reply Quote 0
    • S
      studiouszebra M0★ M1
      last edited by Apr 12, 2022, 9:46 AM

      See I don't have module 5 but I know some mod.
      27 mod 4 = 3:
      because
      27 = 6 * 4 + 3

      and
      54 = 13 * 4 + 2
      now
      54 = 27 + 27 = (6 * 4 + 3) + (6 * 4 + 3)
      54 = (6 * 4 ) + (6 * 4 ) + (3 + 3)
      54 = (6 * 4 ) + (6 * 4 ) + 4 + 2
      54 = 4( 12 + 1) + 2

      54 = 13 * 4 + 2
      And I don't know Professor said that but I thought this would work.
      Sorry if I misunderstood.

      1 Reply Last reply Reply Quote 1
      • P
        pulleybear M0 M1 M2 M3 M4 M5 @Bella
        last edited by Apr 20, 2022, 8:43 PM

        @Bella Both are actually correct. I believe Professor Loh first found 27 (mod 4) to be 3, and then doubled this to get 6. Professor Loh is emphasizing the simplification step, which makes working with larger numbers easier. And if we simplify this further, 6 is 2 (mod 4). So your calculator is not wrong; 27 + 27 is 2 (mod 4). But noting Professor Loh's strategy will help you solve these types of problems more efficiently 🙂

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