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Find the sum of the arithmetic progression
4 + 9 + 14 + 19 + …….94 + 99 + 104

  • math -

    first you have to know how many terms you have
    what term is 104
    a + (n-1)d = term(n)
    4 + (n-1)(5) = 104
    5n - 5 = 100
    5n = 105
    n = 21

    now sum(21) = (first + last)(21/2)

    =(4+104)(21/2) = 1134

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