Question

find the sum of all natural number between 600 and 900 which are divided by 4​

Answer 1

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Sum of all natural numbers between 400 and 600 that are divisible by 9 are:-

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