Question

    What should come in place of the question mark (?) in the following number series?    

    15         12        ?          9         21         6

    A 18 Correct Answer Incorrect Answer
    B 15 Correct Answer Incorrect Answer
    C 17 Correct Answer Incorrect Answer
    D 19 Correct Answer Incorrect Answer
    E 12 Correct Answer Incorrect Answer

    Solution

    15 – 3 = 12 12 + 6 = 18 18 – 9 = 9 9 + 12 = 21 21 – 15 = 6

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