Question

find thesum of all the natural no from 1 to 1000which are not divisible by 5​

Answer 1

Step-by-step explanation:

Sum of natural numbers

n ( n+1) / 2

Sum of natural numbers between 1 to 1000

2 + 3+ .......+ 999

[999 x ( 999+1) / 2 ] - 1

Since it starts from 2

499500 - 1 = 499499

Div by 5

5+10+.........+ 995

5 ( 1+2+.......+ 199)

5 [ 199 x ( 199 + 1)] / 2

5 x 100 x 5

99500

499499 - 99500

399999