Question

How do you calculate the sum of odd numbers between 1 and 2001?

Answer 1

Refer to explanation

Explanation:

How many odd numbers are between 1 and 2001?

They form a sequence which general formula is

`a_n=a+(n-1)*d=>1999=3+(n-1)*2=>n=999`

Their sum is

`S=n/2*(a_1+a_n)=999/2*(3+1999)=>S=999999`