You can solve this problem by using the Gauss method. The Gauss method is a method where you can add the first and last numbers together, and then multiply by how many times that appears. Here, the sum of the first and last number is -11. In this sequence, it would appear ten times (since there are ten terms and the terms are used twice in every eleven). -11 * 5 is -55, so that means the answer to this question is -55.
