Posted by Riana on Tuesday, January 1, 2013 at 7:56pm.
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 - Reiny, Tuesday, January 1, 2013 at 8:03pm
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 - Riana, Tuesday, January 1, 2013 at 8:15pm
how did you gt 19d ?
math - Reiny, Tuesday, January 1, 2013 at 8:23pm
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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