what is the sum of the odd numbers 1-2009

Answer 1

number of terms ---- n
a=1
term(n) = a + (n-1)d
2009 = 1 + (n-1)2
2009 = 1 + 2n - 2
2n = 2010
n = 1005

sum = (1005/2) (1 + 2009) = 1010025