Question

find the sum of all number between 400 to 600 which are divisible by 7. step by step pls​

Answer 1

Step-by-step explanation:

S=405 + 414 + 423 + 432 +,……………………….+594.

This is an A.P. in which a = 405 , d= 9 , tn= 594 , n=?

tn=a+(n-1).d

594=405+(n-1).9

594–405 =(n-1).9

189/9=(n-1)

21+1 = n

n= 22

Sn= n/2.[2.a+(n-1).d]

S22 =22/2.[2.405+(22–1).9]

S22= 11.[810+189] = 11×999 = 10989. Answer.