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    Question

    Find the unit digit of the expression: 7! + 8! + 9! +

    10! + ........ + 500!.
    A 5 Correct Answer Incorrect Answer
    B 3 Correct Answer Incorrect Answer
    D 8 Correct Answer Incorrect Answer

    Solution

    1! = 1 2! = 1 X 2 = 2 3! = 1 X 2 X 3 = 6 4! = 1 X 2 X 3 X 4 = 24 5! = 1 X 2 X 3 X 4 X 5 = 120 6! = 1 X 2 X 3 X 4 X 5 X 6 = 720 Here, we can observe that the unit-digit of numbers larger than 4! Is 0. So, unit digit of the given expression, 7! + 8! + 9! + 10! + ........ + 500! = unit digit of (0 + 0 + 0 + ........ + 0) = unit digit of 0 Required unit digit = 0

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