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    Question

    The 5th and 8th term of an arithmetic progression are 13 and -5 respectively. What is the 15th term?

    A −23 Correct Answer Incorrect Answer
    B −53 Correct Answer Incorrect Answer
    C −73 Correct Answer Incorrect Answer
    D −43 Correct Answer Incorrect Answer

    Solution

    Let the first term of an AP = a & the common difference = d 5th term of AP = A5 = a + 4d = 13----------(i) 8th term = A8 = a + 7d = - 5 --------(ii) Subtracting equation (i) from (ii), we get: => 7d − 4d = −5 − 13 =>3d = -18 => d = -18/3 = - 6 Substituting it in equation (i), => a = 13 − 3(−6) = 13 + 18 = 31 ∴ A15 = a + 14 d = 31 + 14(-6) = 31 − 84 = −53

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