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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 -47 Correct Answer Incorrect Answer
    C −73 Correct Answer Incorrect Answer
    D −43 Correct Answer Incorrect Answer

    Solution

    Given: 5th term a5 = 13, 8th term a8 = −5.

    Use the formula: The formula for the n-th term is:

    Solve the system of equations: Subtract the first equation from the second: 3d = −18 ⇒ d = − 6 Substitute d = − 6 into a1+ 4d = 13:

    Find the 15th term:

    The 15th term is -47.

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