What is the sum of the 12th to 20th terms (inclusive) of the arithmetic sequence 7,12,17,22,...?
A
516
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B
676
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C
117
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D
667
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Solution
The correct option is B676 First term a=7d=5 We know the formula, Sn=n2[2×a(n−1)d] S12=122[2×7+(12−1)5] S12=414 S20=202[2×7+(20−1)5] S20=1090 Therefore the sum of the 12th to 20th terms =1090−414=676