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    Question

    Let ‘x’ be the least number divisible by 18, 20, 27,

    30, and 50, and also ‘x’ is a perfect square. Find the remainder when ‘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 × 3²

    20 = 2² × 5

    27 = 3³

    30 = 2 × 3 × 5

    50 = 2 × 5²

    LCM (take highest powers)

    LCM = 2² × 3³ × 5² = 2700

    Make it a perfect square

    2700 = 2² × 3³ × 5² → exponent of 3 is odd

    Multiply by 3 to make exponent of 3 even:

    x = 2700 × 3 = 2² × 3⁴ × 5² = 8100

    Remainder when x is divided by 77

    8100 ÷ 77 → 77 × 105 = 8085

    8100 − 8085 = 15

    Remainder = 15

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