Question

Tas
8. The sum of all numbers between 200 and
400 which are divisible by 7 are?
(A) 8729
(B) 6730
7000​

Answer 1

Answer:

a.8729

please mark as brainliest

Answer 2

The numbers lying between 200 and 400, which are divisible by 7, are

203, 210, 217, ­­­­­­­­… 399

∴First term, a = 203

Last term, l = 399

Common difference, d = 7

Let the number of terms of the A.P. be n.

∴ an = 399 = a + (n –1) d

⇒ 399 = 203 + (n –1) 7

⇒ 7 (n –1) = 196

⇒ n –1 = 28

⇒ n = 29

Sn = n/2(a+l)

= 29/2(203+399)

= 29×602/2

= 29 × 301

= 8729.........