What is the sum of all the odd integers between $300$ and $500$?

301 + 303 + 305 + 307 + … + 497 + 499

301 * 100 + 2(1+2+3+4+…+98+99)

30100 + 2(99)(100)/2

30100 + 9900

40000

There are 100 odd numbers in the interval    sum = 100/2 (301 + 499) = 40 000