14 of 15 > Experiments on learning in animals sometimes measure how long it takes mice to find their way through a maze. The mean time is 18 seconds for one particular maze. A researcher thinks that a loud noise will cause the mice to complete the maze faster. She measures how long each of 10 mice takes with a noise as stimulus. The sample mean is x = 16.5 seconds. The null hypothesis for the significance test is O HO : H < 16.5. O HO : M = 16.5. OHO : M = 18. OHO : M < 18