The mean work week for engineers in a start-up company is believed to be about 65 hours. A newly hired engineer hopes that it's shorter. She asks 10 engineering friends in start-ups for the lengths of their mean work weeks. Their responses are 70; 45; 55; 60; 65; 55; 55; 60; 50; 55. Is the newly hired engineer testing a mean or a proportion? mean proportion The null hypothesis, in symbols, is = Is the test left-tailed, right-tailed, or two-tailed? left-tailed right-tailed two-tailed O O O