Question
What is the common difference of an AP which has its first term as 100 and the sum of its first 6 terms = 5 times the sum of its next six terms?
Answer: Option C
:
C
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C
Option a and b can be eliminated directly, as from the statement sum of its first 6 terms = 5 times the sum of its next six terms, we can deduce that the Common Difference is negative (decreasing AP).
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Take option c
Sum to 1st 6 terms is given by the formula n2(2a+[n−1]d)
= 3(200-50)= 450
Sum to 2nd 6 terms = Sum to 12 terms – sum to 6 terms
= 6( 200-110) -450
= 540 – 450 = 90
5 × Sum to 2nd 6 terms = 450
Hence option c
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