What do you get by adding all the numbers from 1 to 200? To answer this question think about these questions first:
a. What is the sum of the first number and the last number?
b. What is the sum of the second number and the second to last number?
c. What is the sum of the third and the third to the last number?
d. If you pair up all the numbers as suggested above, how much does each pair add to and how many pairs are there?
Now you should be able to answer the original question.