Posted by Anonymous on Monday, December 27, 2010 at 10:17am.
A pile of bricks has 85 bricks in the bottom row, 81 bricks in the second row up, 77 in the third, and so on up to the top row that contains only 1 brick. How many bricks are in the 12th row?
I don't know if I'm right but I attempted this problem below
c = a1  d
c = 85  4 = 81
 85 + 81 = 166
Sn = n / 2 (a1 + an)
Sn = 85 / 2 (85 + 166)
Sn = 10667.5

Math  Dr Russ, Monday, December 27, 2010 at 10:30am
I can't follow you calculation.
Row 1 has
85
Row 2 has
81
row 3 has
77
The nth row will have
854(n1)
so if n=12
then
854(121)=8544=41 bricks

Math  Anonymous, Monday, December 27, 2010 at 10:42am
Right, instead of using the Sn formula. I could have just use an = a1 + (n  1) d
Thanks a lot
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