Math sequence

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The sum of the first 5 terms of an arthmetic sequence, is 30 and the sum of the next 4 terms is 69 .
Find the arthemetic progression?

  • Math sequence -

    so the sum of the first 9 terms would be 99

    sum(5) = 30 ---> (5/2)(2a + 4d) = 30
    5(2a+4d) = 60
    2a + 4d = 12
    a + 2d = 6

    sum(9) = 99 ----> (9/2)(2a + 8d) = 99
    2a + 8d = 22
    a + 4d = 11

    subtract them
    2d = 5
    d = 5/2 or 2.5
    then a = 1

    the arithmetic sequence is
    1 , 3.5, 6, 8.5 , ...

  • Math sequence -

    What is lhe sum of lhe first 12 terms of an A.p whose first term is 15 and common difference is 13.

  • Math sequence -

    1038

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