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The sum of the first 20 terms of the AP 5, 9, 13, 17, ... is ?

Competition practiceAlgebra

A820
B840
C860
D880

Step-by-Step Solution

Here

a = 5, d = 4, n = 20

. Sum =

(n /2) [2 a + (n - 1) d] = 10 [10 + 76] = 10 \times 86 = 860

.

Answer: C) 860

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