Math
posted by Matt capili .
A pile of blocks has 40 blocks in the bottom row 36 blocks in the second row 32 blocks in the third row and so on until there are only 4 blocks on the top row how many blocks? Are there in the 7th row? How many blocks are there in all

Math 
Anonymous
(404)/4 = 9
so, there are 9 rows after the 1st, making 10 in all.
On the nth row, there are
40(n1)*4 = 444n bricks
The sum of n rows, Sn, with
a = 40
d = 4
is
Sn = n/2 (2*40  (n1)*4) = 2n(21n)
Now you can answer the questions. 
Math 
Julian Gayle
135
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