Question

Find the sum of all natural number between 200
and 400, which are dinsible by 7.​

Answer 1

Answer:

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Answer 2

Answer:

Step-by-step explanation:

Natural numbers between 200 and 400 divisible by 7-

203,210,217,.....,399

The above series forms A.P. with first term 203 and common difference 7.

Also,

Last term =399

Now, An  =a+(n−1)d

399=203+(n−1)7

⇒n−1=  399−203 /7

⇒n=28+1=29

Therefore,

Sn  = n  /  2(a+l)

⇒S29 =  29/2   (29+399)

⇒S 29  =29 /  2 ×328=29×164=4756