Question

find the sum of all numbers between 200 and 400 which are divisible by 7.... ?​

Answer 1

8729is ur answer

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Answer 2

★ Given :

A.P : 203, 210, 21 ........ 399

First term (a) = 203

Common Difference (d) = 7

Last term (An or L) = 399

$\rule{200}{1}$

★ To Find :

We have to find the sum of all number between 200 and 409 which are divisible by 7.

$\rule{200}{1}$

★ Solution :

We know that,

An = a + (n - 1)d

→ 399 = 203 + (n - 1)7

→ 399 - 203 = (n - 1)7

→ 196 = (n - 1)7

→ n - 1 = 196/7

→ n - 1 = 28

→ n = 28 + 1

→ n = 29

$\rule{200}{2}$

Sn = n/2 (a + L)

→ Sn = 29/2 (203 + 399)

→ Sn = 29/2 * 602

→ Sn = 29 * 301

→ Sn = 8729