Question

Find the sum of all even natural numbers from 2 to 40 by using the formula​

Answer 1

Answer:

Sn=n2(a+l) , where l=a+(n−1)d. Hence,

the sum of all even natural numbers from 2 to 40 is equals to 420.

Answer 2

Step-by-step explanation:

To solve this question, firstly we will find the number of even numbers from 2 to 40 by using formula of finding nth term of an A.P. When last term is given, a = 2, l = 40

We know that, nth term of an A.P when last term is given can be find by the formula

l = a + ( n - 1 ) d

40 = 2 + ( n - 1 ) 2

40 - 2 = (n - 1) 2

38 = ( n - 1 ) 2

n - 1 = 19

n = 19 + 1

n = 20

So, there are total 20 even numbers from 2 to 40.

we know that, the sum of terms of A.P is given by the following formula.

Sn = n/2 ( a+ l)

S20 = 20/ 2 (2 + 40)

S20 = 10 × 42

S20 = 420