Find the sum of the first 20 odd natural numbers by AP method.

Answer: The sum of the first 20 odd natural numbers is 400.

  • Natural numbers are part of the number system that comprises all the positive integers from 1 to infinity and are often used for the purpose of counting.
  • Zero not include in natural numbers. In reality, 1,2,3,4,5,6,7,8,9…. are known as counting numbers.
  • Natural numbers are real numbers, which only contain positive integers, i.e. 1, 2, 3, 4,5,6, ………. With zero, fractions, decimals, and negative numbers excluded.

The first 20 odd natural numbers are given by 1,3,5,7,9……,37,39 and this forms an AP.

a = 1

d = 2

n = 20

The formula of sum of an A.P series

S = n/2[2a + (n − 1) × d]

S = 20/2 [2 × 1 + (20 – 1) 2]

S = 10[2 + 38]

S = 400

The sum of first 20 odd natural numbers is 400

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