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math

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bricks are stacked in 20 rows such that each row has a fixed number of bricks more than the row above it. the top row has 5 bricks and the bottom row 62 bricks. how many bricks are in the stack?

  • math -

    using your arithmetic sequence definitions

    t1 = a = 5
    t20 = a+19d = 62

    5+19d = 62
    19d = 57
    d = 3

    sum(20) = (20/2)(first + last)
    = 10(5+62) = 670

  • math -

    how did you gt 19d ?

  • math -

    The formula for
    term(n) = a + (n-1)d
    so term(20) = a+19d

    You MUST know these to be able to work with sequences

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