Algebra

What is the sum of the geometric series 20 + 21 + 22 + 23 + 24 + … + 29?

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  1. https://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html
    a= 20
    d = 1
    or just figure it out
    say it was just 20, 21, 22, 23
    the number of terms is 1+ 23-20 = 4
    the average is 21.5
    4*21.5 = 86
    check --- sure enough 86
    so now this hard one 20,21 .... 29 number of terms = 1 + 29 -20 = 10
    average = 49/2 = 24.5
    so 10 * 24.5 = 245

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