This document describes a famous story about the German mathematician Karl Friedrich Gauss. When Gauss was 10 years old, his teacher posed the question "What is the sum of 1 + 2 + 3 + ... + 98 + 99 + 100?" to the class. Gauss immediately wrote down the correct answer without showing any working. The document then provides additional context about Gauss and his shortcut formula to solve the problem, as well as examples of using the formula to find sums of arithmetic sequences.