Find the sum of the first 20 terms of the A.P. 3, 7, 11, 15, .....
Q.2 (B)(iv) Find the sum of the first 20 terms of the A.P. 3, 7, 11, 15, .....
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Answer: \(S_{20} = 820\)
\(a = 3,\ d = 4,\ n = 20\).
\(S_n = \dfrac{n}{2}[2a + (n - 1)d]\)
\(S_{20} = \dfrac{20}{2}[2(3) + 19(4)] = 10[6 + 76] = 10 \times 82 = 820\).
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· 27 Oct 2026
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