Vinatieri Valves Inc. stock produced returns of 22 percent, -5 percent, 16 percent, 4 percent, and -2 percent over the past five years, respectively. What is the 99 percent probability range of returns? Round your answer to one decimal place. For example, 1,234.5678 is 1,234.6.

For the percent probability range of returns, I know that the rate has to be added and subtracted from (3*standard deviation). Can you tell me what this 3 represents? I am confused.