Is the mean age at which American children learn to walk les

Is the mean age at which American children learn to walk less than 15 month? A study of 40 American children found a mean walking age of x = 13.2 months. If the population of all American children is Normally distributed with mean age mu until they begin to walk and standard deviation sigma, which of the following null and alternative hypotheses should we test to answer this question? H0: mu = 13.2 vs.H0: mu

Solution

We Look for \"less than 15\", which is depicted in alternative hypothesis in only option (D)