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The sum of the first 20 odd natural numbers is (a) 100 (b) 210 (c) 400 (d) 420 |
Answer» Correct answer is (c) 400 The first 20 odd natural numbers are 1, 3, 5,.., 39. These numbers are in AP. Here. a = 1, l = 39 and n = 20 ∴ Sum of first 20 odd natural numbers = \(\frac{20}{2}(1+39)\) [\(S_n=\frac{n}{2}(a+l)\)] = 10 x 40 = 400 |
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