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Find the sum:- 7+10½+14...+84

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Find the sum:- 7+10½+14...+84

    • Posted by Mohit Gothwal 1 year, 4 months ago

    CBSE > Class 10 > Mathematics
    • 3 answers

    Khwahis Parveen 1 year, 4 months ago

    7+10½+14+........+84 Now first find the n By the formula, An=a+(n-1)×d Here, An =84 a=7 and d = 7/2 Put the value 84=7+(n-1)×7/2 84=7+7/2n-7/2 84=7/2+7/2n 84-7/2=7/2n 161/2=7/2n n=23 Sn=n/2(a+l) Sn=23/2(7+84) Sn=23/2×91 Sn=2093/2 Sn=1046.5 OR Sn=1046½

    1Thank You

    Mohit Gothwal 1 year, 4 months ago

    No... I can't find the answer by this shall we use n/2 (a+l)

    0Thank You

    Saurav Kumar Dwivedi 1 year, 4 months ago

    Apply the formula of Sn term = n/2(2a +(n-1)d) of arithmetic progression you will definitely get answer

    0Thank You

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