Question

Find sum of all natural numbers betwewn 1 to 1000 neither divisible by 2 nor by 5

Answer 1

Answer:

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

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