The weight in pounds for a population of school-aged children is normally distributed with a mean equal to 135 20 pounds ( ). Suppose we select a sample of 100 children (n= 100) to test whether children in this population are gaining weight at a 0.05 level of significance. a) what is the null hypothesis? b) what is the critical value for this test? c) what is the mean of the sampling distribution? d) what is the standard error of the mean for the sampling distribution?