Question Bank • QB_EXP_GA_ALG_001 NAT • 1 Mark

Section 8: General Aptitude

Quantitative: Algebra, Functions & Progressions

Subtopic: Sum of arithmetic progression series

Question Statement:

The first term of an arithmetic progression is $a = 3$ and the common difference is $d = 4$. The sum of the first $20$ terms ($S_{20}$) of this series is ________.

Answer Key:

820

Step-by-Step Solution & Explanation

The sum of an arithmetic progression is: $S_n = \frac{n}{2} [2a + (n - 1)d]$ Given $a = 3$, $d = 4$, and $n = 20$: $S_{20} = \frac{20}{2} [2(3) + (20 - 1)(4)] = 10 [6 + 19(4)] = 10 [6 + 76] = 10 [82] = 820$
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