Question 1209331
The given series is 1-2+3-4+5-6+.....+2007-2008+2009-2010+2011

The given series is equivalent to (1+3+5+........+2011)-(2+4+6+........+2010)

We can use Google Sheets and Excel to solve the given problem.

I have attached a snippet of the Excel sheet.

Answer=1006