MCQ - 452-9184

Correct Answer: C

Explanation:

Sum of first 20 odd natural numbers is 1 + 3 + 5 + 7 + … + 39.
This forms an arithmetic series with first term = a = 1
and common difference = d = 2
Sum of n terms of this arithmetic series is given by:
S_n =$\genfrac{}{}{1px}{}{\mathrm{n}}{2}$ [2a + (n - 1)d]
Therefore sum of 20 terms of this arithmetic series is given by:
∴ S₂₀ =$\genfrac{}{}{1px}{}{20}{2}$ [2(1) + (20 - 1)(2)]
= 10 [2 + 38]
= 10 × 40
= 400