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a pile of bricks has 85 bricks in the bottom row, 79 bricks in the second row, 73 in the third row, and so on until there is only 1 brick in the top row.

how many bricks are in the 12th row?

how many rows are there in all?

  • MATH -

    You have an arithmetic sequence where
    a = 85 , d = -6

    12th row = 85 + 11(-6) = 19

    row(n ) = a + (n-1)d
    1 = 85 + (n-1)(-6)
    1 = 85 - 6n + 6
    6n = 90
    n = 15
    there are 15 rows

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