The numbers between 200 and 400 which are divisible by 7 are 203, 210, 217,......, 399.
This sequence forms an A.P., whose first term is 203 and difference is 7.
Let 399 be the nth term of sequence, then
399 = 203 + (n – 1) 7 ⇒ (n – 1) 7 = 399 – 203
⇒ (n – 1)7 = 196 ⇒ n – 1 = 28 ⇒ n = 29
Hence, total number of terms in A.P. are 29.
∴ Sum of 29 terms =

29

2

[2 (203) + (29 - 1) 7]
i.e., S29 [406 + 196] =

29

2

× 602 = 8729