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Deepak Bora
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Find the number of terms in the given series of an A.P.

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This question is from NCERT Book class 10th Ch. number 5 Ex. 5.2 Q. 5 (ii). In the following question you have to find the number of terms in the given series and give its solution briefly.

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  1. Solution:

    a = 18

    d = a2-a

    d = (31-36)/2 = -5/2

    Let n terms be in this A.P.

    an = 205

    For an A.P we know:-

    an = a+(n−1)d

    -47 = 18+(n-1)(-5/2)

    -47-18 = (n-1)(-5/2)

    -65 = (n-1)(-5/2)

    (n-1) = -130/-5

    (n-1) = 26

    n = 27

    The A.P. has 27 terms in its given series.

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