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    Question

    If '63a9b' is a five-digit number which is divisible by 72,

    then find the value of (a + 2b).
    A 20 Correct Answer Incorrect Answer
    B 12 Correct Answer Incorrect Answer
    C 24 Correct Answer Incorrect Answer
    D 18 Correct Answer Incorrect Answer

    Solution

    ATQ,

    Since, 72 = 9 × 8

    So, the given number must be divisible by both 9 and 8.

    Divisibility by 8:

    Last three digits of the number (a9b) must be divisible by 8.

    For a = 4 and b = 8, the number "498" is divisible by 8.

    Divisibility by 9:

    Sum of the digits (6 + 3 + 4 + 9 + 8 = 30) must be divisible by 9, which it is not.

    Adjusting the values, for a = 6 and b = 3, the number "693" is divisible by both.

    Hence, a = 6, b = 3

    And, a + 2b = 6 + 2 × 3 = 6 + 6 = 12

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