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Pure Mathematics
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Topic Topic: The fourth term of an Arithmetic Progression is... Post ReplyNew Question
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System
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Joined: 26 June 2005
Posts: 918
Posted: 20 November 2005 at 1:34pm | IP Logged Quote System

QUIZ QUESTION #1642
The fourth term of an Arithmetic Progression is 8 and the sum of the first 12 terms is 126. Find the sum of the next 8 terms.
    A.   163
    B.   157
    C.   160
    D.   164
 QUIZ QUESTION #1642 created by Tutor11744 on 06 November 2005 at 12:22pm

Correct answer: D    Correct clicks: 29.39%  Wrong clicks: 70.61%
 
    A.   [31 clicks 11.83%] 
 
    B.   [67 clicks 25.57%] 
 
    C.   [87 clicks 33.21%] 
 
    D.   [77 clicks 29.39%] 
 
Please discuss this quiz question.
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Jdoezzzzzzzzzz
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Joined: 04 October 2006
Posts: 4
Posted: 04 October 2006 at 10:30am | IP Logged Quote Jdoezzzzzzzzzz

formula- [(first term +last term) x #number of terms]/2=sum

let first term= f

f f+x f+2x f+3x f+4x= 8 f+5x.. f+11x (12th term)...f+19x(20thterm)

(f+f+11x)12/2=126

combine like terms to get 2f+11x=21

f+3x=8, change to f=8-3x

plug in value of  f from the second equation into the first

2(8-3x)+11x=21

solve to get x=1

solve for f now by plugging 1 into f=8-3x

f=8-3(1)  f=5

find the 20th term f+19x

=5+19(1)=24

solve for the sum of the 1st 20 with the formula to get 290

subtract the sum of the 1st 12 terms  (126) to get 164

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