earthquake magnitude

Question

Early in the century the earthquake in San Francisco registered 8.3 on the Richter scale. In the same year, another earthquake was recorded in South America that was four time stronger. What was the magnitude of the earthquake in South American?

Answer 1

4 * 8.3 = 33.2. The answer is 33.2 because the known earthquake was 8.3 in magnitude. Since the unknown is 4 times stronger than the known, I multiplied by 4.