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

Solution:

The numbers lying between 200 and 400 which are divisible by 7 are 203, 210, 217, ...., 399.

Here, a = 203, d = 7 and an = 399

Therefore,

a_n = a + (n - 1) d

399 = 203 + (n - 1)7

⇒ (n - 1)7 = 196

⇒ n - 1 = 28

⇒ n = 29

Hence,

S₂₉ = 29/2 (203 + 399)

= 29/2 (602)

= 29 x 301

= 8729

Thus, the required sum is 8729

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NCERT Solutions Class 11 Maths Chapter 9 Exercise ME Question 4

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

Summary:

Therefore the sum of all numbers between 200 and 400 which are divisible by 7 comes out to be 8729 using S₂₉ = 29/2 (203 + 399)