Jojo J.

asked • 10/06/18

how to solve it?

A 12 wheeler truck is loaded with 13 piles of log. The bottom row contains 25 logs. Each of the remaining piles contains 2 logs less than the number of logs on a pile directly below it. Find the total weight of the logs carried by the truck if each log weighs 57 kg

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Inactive Tutor answered • 10/06/18

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Sum up the number of logs.
Multiply the sum by 57
 
(25+23+21+19+17+15+13+11+9+7+5+3+1)57 = ______ kg
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Jojo J.

is it an aarithmetic series?
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10/08/18

Inactive Tutor

Yes.  Arithemetic series with 13 terms, common difference d -2, a1 = 25
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10/08/18

Inactive Tutor

starting at a1 = 25, d=-2, n=13
 
an = a1 + (n-1)d
a13 = 25 + (13-1)(-2) = 25 + 12(-2) = 25 -12 = 1
 
sn = n(a1 + an)/2
s13 = 13(25+1)/2 = 338/2 = 169
 
169(57) = 9633 kg
 
****************************************
(25+23+21+...1)(57) = 169
169(57) = 9633 kg
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10/08/18

Jojo J.

why is the common difference is -2? :( 
 
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10/09/18

Jojo J.

why is the common difference is -2?
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10/09/18

Jojo J.

I already know now, :) thank you very much <3
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10/09/18

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