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      Question

      Let β€˜y’ be the smallest number divisible by 12, 20,

      28, and 42, such that β€˜y’ is a perfect square. What will be the remainder when β€˜y’ is divided by 97?
      A 12 Correct Answer Incorrect Answer
      B 14 Correct Answer Incorrect Answer
      C 16 Correct Answer Incorrect Answer
      D 62 Correct Answer Incorrect Answer

      Solution

      Prime factors 12 = 2Β² Γ— 3 20 = 2Β² Γ— 5 28 = 2Β² Γ— 7 42 = 2 Γ— 3 Γ— 7 LCM LCM = 2Β² Γ— 3 Γ— 5 Γ— 7 = 420 Make it a perfect square 420 = 2Β² Γ— 3ΒΉ Γ— 5ΒΉ Γ— 7ΒΉ β†’ need to multiply by 3 Γ— 5 Γ— 7 = 105 β†’ y = 420 Γ— 105 = 44100 = 210Β² Find remainder when divided by 97 210 ≑ 16 (mod 97) So y = 210Β² ≑ 16Β² = 256 ≑ 62 (mod 97) Final Answer: 62

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