1. What does the standard deviation measure?

2. Biologists gather data on a sample of fish in a large lake. They capture, measure the length of, and release 1,000 fish. They find that the standard deviation is 5 centimeters, and the mean is 25 centimeters. They also notice that the shape of the distribution (according to a histogram) is very much skewed to the left (which means that some fish are smaller than most of the others). Approximately what percentage of fish in the lake is likely to have a length within one standard deviation of the mean? Interpret the result.