Algebra-Please help

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We're working on geometric and athrimetic series and I really don't know where to start with this except that t sub 1 = 101
How would I find the sum of the multiples of 5 between 101 and 2001 help

  • Algebra-Please help -

    well, the first multiple of 5 in that interval is 105.
    The last is 2000.
    105 + 110 + 115 + ........ 2000
    n-1 = (2000-105)/5 = 379
    n = 380

    Sum = (n/2)(a1+an) = (380/2)(2105)
    =399,950

  • Algebra-Please help -

    Thank you very much

  • Algebra-Please help -

    You are welcome :)

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