1.Suppose the weight of adult green sea urchins (strongylocentrotus dreobachiensis) is approximately

normally distributed with a mean of 48.0 grams and a standard deviation of 18.0 grams. The 30th

percentile of weight of adult green sea urchins is closest to which one of the following?

(a) 33

(b) 36

(c) 39

(d) 42

(e) 57

2.In the inference procedures used in this course, we have sometimes used the t distribution, and

sometimes the standard normal distribution. Consider the following four statements that relate

to these two distributions.

I. In inference procedures for a single population mean , the t distribution should be used

when the population variance is known.

II. The variance of the t distribution is greater than that of the standard normal distribution.

III. The t distribution tends toward the standard normal distribution as the degrees of freedom

increase.

IV. The standard normal distribution is symmetric about 0, but the t distribution is not.

How many of these statements are true?

(a) 0

(b) 1

(c) 2

(d) 3

(e) 4