According to an avid aquarist, the average number of fish in a 20-gallon tank is 10, with a standard deviation of two. His friend, also an aquarist, does not believe that the standard deviation is two. She counts the number of fish in 15 other 20-gallon tanks. Based on the results that follow, do you think that the standard deviation is different from two at the 5% level? Data: 11; 10; 9; 10; 10; 11; 11; 10; 11; 9; 7; 10; 11; 10; 11.