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    Question

    The following expressions form a series followed by a (?). Find the odd one out first and then find that what will come in place of the question mark (?) according to the corrected series?

    (x - 10), (x + 10), 120, x(x - 10), 4500, (1540 ×  x), ?

    Also, 'x' = positive root of x2 - 6x - 720 = 0

    A (20020 × x) Correct Answer Incorrect Answer
    B (20120 × x) Correct Answer Incorrect Answer
    C (20320 × x) Correct Answer Incorrect Answer
    D (20420 × x) Correct Answer Incorrect Answer
    E (20220 × x) Correct Answer Incorrect Answer

    Solution

    Given, x2 - 6x - 720 = 0 Or, x2 - 30x + 24x - 720 = 0 Or, x(x - 30) + 24(x - 30) = 0 Or, (x - 30)(x + 24) = 0 So, x = 30 or x = -24 So, x = 30 So, (x - 10) = 20 (x + 10) = 40 (x - 10) × x = 20 × 30 = 600 (1540 × x) = 1540 × 30 = 46200 So, the series becomes: 20, 40, 120, 600, 4500, 46200, ? The series follows the pattern as: 20 × 2 = 40 40 × 3 = 120 120 × 5 = 600 600 × 7 = 4200 4200 × 11 = 46200 So, 4200 should come in place of 4500. And, ? = 46200 × 13 = 600600 Or, 600600 ÷ 30 = (20020 × x)

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