Find the sum of all numbers between 200 and 400 which are divisible by 7.

Asked by Abhisek | 1 year ago |  66

##### Solution :-

First let’s find the numbers between 200 and 400 which are divisible by 7.

The numbers are:

203, 210, 217, … 399

Here, the first term, a = 203

Last term, l = 399 and

Common difference, d = 7

Let’s consider the number of terms of the A.P. to be n.

Hence, an = 399 = a + (n –1) d

399 = 203 + (n –1) 7

7 (n –1) = 196

n –1 = 28

n = 29

Then, the sum of 29 terms of the A.P is given by:

$$s_n=\dfrac{29}{2}(203+399)$$

$$\dfrac{29}{2}(602)$$

= (29)(301)

= 8729

Therefore, the required sum is 8729.

Answered by Pragya Singh | 1 year ago

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