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Find the sum of the first 20 terms of the arithmetic progression: 3, 7, 11, 15, ...

Competition practiceAlgebra

A820
B800
C780
D840

Step-by-Step Solution

Here

a = 3, d = 4, n = 20

. Sum =

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

.

Answer: A) 820

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