Partial solutions to Midterm 2

Because you were given the right answers to all midterm questions as soon as you completed the exam, here I will give only the answers to questions that were frequently missed or that required computations.

Question 1

Many students missed the part on experimental units.  See Lecture 8, slide 2, which defines experimental units as the   individual itemson which an experiment is done.  Experimental units are usually called subjects when they are human.  We can measure a response variable individually on each experimental unit.  Thus, depending upon which version of Question 1 you got, the experimental units were either individual students or individual tomato plants.

Question 2

The distribution of a continuous variable in a population is normal with mean mu = 1.206 and standard deviation sigma = 5.  A simple random sample of size 13 is drawn from this population.  What is the probability that the sample mean xbar is greater than 1.952?  (Numeric answer, accurate to 3 digits)

The sampling distribution of xbar is Normal with mean mu and standard deviation sigma / sqrt(n)

We need to standardize 1.952 as a draw from this distribution.

z = (1.952 - 1.206) / ( 5 / sqrt(13) ) = 0.5379

Table A tells us that the probability of getting a standard normal value less than 0.54 is 0.7054.  To get the probability of getting a standard normal larger than 0.54, we need

1-0.7054 = 0.295