Sequences And Series — Easy JEE math MCQ
The sum of the first 20 terms of an arithmetic progression with first term 5 and common difference 3 is:
- A. 570
- B. 670
- C. 770
- D. 870
Solution
For an AP with first term \(a\) and common difference \(d\), the sum of first \(n\) terms is:
\[
S_n = \frac{n}{2}[2a + (n-1)d]
\]
Substituting \(a = 5\), \(d = 3\), \(n = 20\):
\[
S_{20} = \frac{20}{2}[2(5) + (20-1)(3)] = 10[10 + 57] = 10 \times 67 = 670
\]
So the correct option is B.