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    Question

    Find the sum of all multiples of 9 between 1 and 100

    (including both ends if applicable).
    A 594 Correct Answer Incorrect Answer
    B 625 Correct Answer Incorrect Answer
    C 770 Correct Answer Incorrect Answer
    D 529 Correct Answer Incorrect Answer

    Solution

    First multiple of 9 in this range: 9 Last multiple less than or equal to 100: 99 Sequence: 9, 18, 27, тАж, 99 (AP with a = 9, d = 9) Number of terms n: 99 = 9 + (n тИТ 1) ├Ч 9 99 тИТ 9 = 9(n тИТ 1) 90 = 9(n тИТ 1) тЗТ n тИТ 1 = 10 тЗТ n = 11 Sum = n/2 ├Ч (first + last) = 11/2 ├Ч (9 + 99) = 11/2 ├Ч 108 = 11 ├Ч 54 = 594 Answer: 594.

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