What is the remainder when the sum of the first 102 counting numbers is divided by 5250?  (The first counting number is 1.)
I know that the sum of the first n counting numbers is n(n+1)/2, so I can use that formula to find the sum of the first 102 counting numbers. Plugging in n = 102, I get 102(103)/2, which is 5253. Now I need to find the remainder when 5253 is divided by 5250. I notice that 5253 is just 3 more than 5250, so the remainder must be 3. 