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    Question

    In an arithmetic progression (A.P.), the 10th term is 32

    and the sum of the first 20 terms is 670. What is the first term of the A.P.?
    A 2 Correct Answer Incorrect Answer
    C 5 Correct Answer Incorrect Answer
    D 8 Correct Answer Incorrect Answer

    Solution

    ATQ, Let first term = a, common difference = d. T10 = a + 9d = 32 ...(1) S20 = (20/2)[2a + (20 − 1)d] = 10(2a + 19d) = 670 => 2a + 19d = 67 ...(2) From (1): a = 32 − 9d. Substitute into (2): 2(32 − 9d) + 19d = 67 64 − 18d + 19d = 67 64 + d = 67 ⇒ d = 3. Then a = 32 − 9×3 = 32 − 27 = 5.

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