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The sum of the first 20 terms of the arithmetic progression 3, 7, 11, ... is

Competition practiceAlgebra

A780
B800
C820
D840

Step-by-Step Solution

With

a = 3, d = 4, n = 20 : S = (n /2) [2 a + (n - 1) d] = 10 \times (6 + 19 \times 4) = 10 \times 82 = 820

.

Answer: C) 820

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