Find the sum of first 20 natural numbers which are divisible by7.
Answers
Answer:
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
n
=
2
n
[2a+(n−1)d]
S_{20}=\frac{20}{2}[2(7)+(20-1)7]S
20
=
2
20
[2(7)+(20−1)7]
S_{20}=10[14+133]S
20
=10[14+133]
S_{20}=10[147]S
20
=10[147]
S_{20}=1470S
20
=1470
Therefore, the average of first 20 natural numbers which are divisible by 7 is 73.5.
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Answer:
- 1470.
Step-by-step explanation:
- The number series 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, . . . . , 140.
- Therefore, 1470 is the sum of first 20 positive integers which are divisible by 7.
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