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Mathematics

Find the sum of first 20 terms of an A.P. whose first term is 3 and the last term is 57.

AP

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Answer

S=n2(a+l)=202(3+57)=10×60=600.S = \dfrac{n}{2}(a + l) \\[1em] = \dfrac{20}{2}(3 + 57) \\[1em] = 10 \times 60 \\[1em] = 600.

Hence, sum of first 20 terms = 600.

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