Question

find the sum of all natural numbers between 1 to 1000 which are not divisible by 5.​

Answer 1

Answer:

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 Divisible by 2 2+ 4+ ...........+ 998 2 ( 1+2+......+ 499) 2 x [ 499 x ( 499+ 1)] / 2 499 x 500 249500 Div by 5 5+10+.........+ 995 5 ( 1+2+.......+ 199) 5 [ 199 x ( 199 + 1)] / 2 5 x 100 x 5 99500 Neither div by 2 nor 5 499499 - ( 99500 + 249500 ) 150499

Step-by-step explanation: