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      Question

      Let β€˜x’ be the least number divisible by 18, 20, 27,

      30, and 50, and also β€˜x’ is a perfect square. Find the remainder when β€˜x’ is divided by 77.
      A 15 Correct Answer Incorrect Answer
      B 28 Correct Answer Incorrect Answer
      C 26 Correct Answer Incorrect Answer
      D 42 Correct Answer Incorrect Answer

      Solution

      ATQ,

      Prime factors

      18 = 2 Γ— 3Β²

      20 = 2Β² Γ— 5

      27 = 3Β³

      30 = 2 Γ— 3 Γ— 5

      50 = 2 Γ— 5Β²

      LCM (take highest powers)

      LCM = 2Β² Γ— 3Β³ Γ— 5Β² = 2700

      Make it a perfect square

      2700 = 2Β² Γ— 3Β³ Γ— 5Β² β†’ exponent of 3 is odd

      Multiply by 3 to make exponent of 3 even:

      x = 2700 Γ— 3 = 2Β² Γ— 3⁴ Γ— 5Β² = 8100

      Remainder when x is divided by 77

      8100 Γ· 77 β†’ 77 Γ— 105 = 8085

      8100 βˆ’ 8085 = 15

      Remainder = 15

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