Question

Find all the sum of natural numbers less than 1000 that are not divisible by 5 and 2

Answer 1

natural numbers less than 1000 that are divisible by 5 and 2 are divisible by 10 are
10,20,30,...990
990=10+(n-1)10
n=99
S=99/2(10+990)=99*500=49500
the sum of natural numbers less than 1000 that are not divisible by 5 and 2
=999*1000/2-49500
=999*500-49500
=499500-49500=450000

Answer 2

Answer:

natural numbers less than 1000 that are

divisible by 5 and 2 are divisible by 10 are

10,20,30,...990

990=10+(n-1)10 n=99

the sum of natural numbers less than 1000 that

S=99/2(10+990)=99*500-49500

are not divisible by 5 and 2

-999*1000/2-49500

=999*500-49500

=499500-49500=450000