Question

find the sum of all odd natural no from 20 to 80.​

Answer 1

$\sf\huge \mathbb{\underline{\underline{{Solution}}}}$

Odd numbers : Those natural numbers which are not divisible by 2 or not the multiples of 2 is called odd numbers.

Odd numbers from 20 to 80 are as follows:

21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79

Here ,total number of terms (n) is 30

first term (a) is 21

last term (l) is 79

Here ,we use Sn formula to find out the sum

Sn= n/2(a+l)

➙Sn= 30/2(21+79)

➙Sn= 15(100)

➙Sn= 1500

Therefore,sum of all odd number from 20 to 80 is 1500.

More information=>

Sn= n/2[ 2a+(n-1)d]

when a is given n is given and last term is not given we use this sum formula.

an= a+(n-1)d

We use this formula to find out the nth term .

Answer 2

Odd numbers : Those natural numbers which are not divisible by 2 or not the multiples of 2 is called odd numbers.

Odd numbers from 20 to 80 are as follows:

21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79

Here ,total number of terms (n) is 30

first term (a) is 21

last term (l) is 79

Here ,we use Sn formula to find out the sum

Sn= n/2(a+l)

Sn= 30/2(21+79)

Sn= 15(100)

Sn= 1500

Therefore,sum of all odd number from 20 to 80 is 1500.

please mark me as brainlist