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11b) Find the sum of 20 terms of the A.P. 12, 15, 18--- |
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Answer» Answer: Step-by-step EXPLANATION: Here, a=12, d=15-12=3, n =20. now, S=n/2(2a+(n-1)d) =20/2(2×12+(20-1)3) =10(24+57) =810. |
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