Question

Find the average of first 20 natural numbers which are divisible by 7

Answer 1

2 are average number which are divisible by 7 and that are 7&14

Answer 2

The average of first 20 natural numbers which are divisible by 7 is 73.5.

Step-by-step explanation:

To find : The average of first 20 natural numbers which are divisible by 7 ?

Solution :

First we find the sum of first 20 natural numbers which are divisible by 7.

i.e. 7,14,21,.... forming an A.P.

Where, first term is a=7

Common difference is d=7

Number of terms n= 20

The sum of n terms of A.P is $S_n=\frac{n}{2}[2a+(n-1)d]$

$S_{20}=\frac{20}{2}[2(7)+(20-1)7]$

$S_{20}=10[14+133]$

$S_{20}=10[147]$

$S_{20}=1470$

The average of first 20 natural numbers which are divisible by 7 is given by,

$A=\frac{S_{n}}{n}$

$A=\frac{1470}{20}$

$A=73.5$

Therefore, the average of first 20 natural numbers which are divisible by 7 is 73.5.

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