How many terms of the series 27+24+21+18+… will add up to 126?
Answers
Answered by
1
Answer:
The answer is 7
Step-by-step explanation:
7 terms will add up to 126
Proof:
27+24+21+18+15+12+9=126
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Answered by
1
Step-by-step explanation:
let the number of terms is n
here 1st term a=27
common difference d=(24-27)= -3
we know,
s=n/2{2a+(n-1)d
126=n/2{2.27+(n-1).(-3)}
=> 126.2=n{54-3n+3}
=> 252=n(57-3n)
=> 252=3n(19-n)
=>252/3=n(19-n)
=> 84=19n-n^2
=> n^2-19n+84=0
=>n^2-12n-7n+84=0
=> n(n-12)-7(n-12)=0
=> (n-12)(n-7)=0
number of terms is 12 or 7
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