There is a cheat way in doing this. 2+200 is 202. Since it is only even numbers, there will be 100 numbers (even) between 2 and 200. So we times 202 by 50 (100/2) and we get 10, 100.
the eveb number from 2. to 100 can be described as an arithmetic sequence with common difference of 2. we can get the sum by using the arithmetic series formula.
