Posted by Anonymous on Sunday, February 21, 2010 at 8:00am.
A brick wall is built by using 2 bricks less in each layer than in the previous one. The wall has m layers and in total 21m+40 bricks are used. If the top layer has only 4 bricks, determine:A) the value of m
b) the total number of bricks in the wall

maths  Anonymous, Sunday, February 21, 2010 at 9:35am
i need to know how to do this one please

maths  Reiny, Sunday, February 21, 2010 at 9:51am
let a = 4
we know d = 2
S_{m} = m/2[8 + (m1)(2)]
21m + 40 = m[3+m]
take over, (I got m=20)
Once you have m, sub into 21m+40 for the sum.

maths  Anonymous, Sunday, February 21, 2010 at 10:13am
thx alot
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