Question

Find the sum of first 20 odd natural numbers by ap

Answer 1

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Answer 2

Answer:

The sum of first 20 odd natural numbers is 400.

Step-by-step explanation:

Given : 20 odd natural numbers.

To find : The sum of first 20 odd natural numbers by A.P

Solution :

The first 20 odd natural numbers are given by :

1,3,5,7,9......,37,39.

These form an A.P with [tex]a_1=1[/tex] , d=2 , n=20

Formula of sum of an A.P series $s_n=\frac{n}{2}[2a_1+(n-1)d]$

Put all the values in the formula,

$s_n=\frac{n}{2}[2a_1+(n-1)d]$

$s_{20}=\frac{20}{2}[2(1)+(20-1)2]$

$s_{20}=10[2+(19)2]$

$s_{20}=10[2+38]$

$s_{20}=10[40]$

$s_{20}=400$

Therefore,The sum of first 20 odd natural numbers is 400.