Question 464325
The sum of all numbers between 1 and n can be found using the equation:n(n+1)/2
So, therefore, the sum of all numbers between 1 and 1000 is 
1000(1001)/2=500500
Likewise, the sum of all numbers between 1 and 9999 is
9999(10000)/2=49995000
Thus, the total of all numbers between 1000 and 9999 is the difference between the  two, or
49995000-500500=49494500
The sum of all the odd integers in that span is roughly 1/2 of all the integers so our answer is
49494500/2=24747250..