06/19/2020 (2011: Countdown Round, Problem 9)

Q: The sum of a set of consecutive integers from -8 to n, inclusive, is 55. What is the value of n?

A: 13

If n is 8, then the sum of the numbers would be 0.

If n is 9, then the sum would be 9.

If n is 10, the sum would be 19.

If n is 11, the sum would be 30.

If n is 12, the sum would be 42.

If n is 13, the sum would be 55. That means n = 13.