Which of the following statements concerning the standard normal curve is/are true (if any)?

a) the area under the standard normal curve to the left of -3 is zero.

b) the area under the standard normal curve between any two z-scores is greater than zero.

c) the area under the standard normal curve between two z-scores will be negative if both z-scores are negative

d) the area under the standard normal curve to the left of any z-score is less than 1.

a. a, b
b. b, d
c. a, c
d. a

Farmers know that driving heavy equipment on wet soil compresses the soil and injures future crops. here are data on the "penetrability" of the same type of soil at two levels of compression. penetrability is a measure of how much resistance plant roots will meet when they try to grow through the soil. compressed soil 2.85 2.66 3 2.82 2.76 2.81 2.78 3.08 2.94 2.86 3.08 2.82 2.78 2.98 3.00 2.78 2.96 2.90 3.18 3.16 intermediate soil 3.17 3.37 3.1 3.40 3.38 3.14 3.18 3.26 2.96 3.02 3.54 3.36 3.18 3.12 3.86 2.92 3.46 3.44 3.62 4.26 use the data, omitting the high outlier, to give a 95% confidence interval for the decrease in penetrability of compressed soil relative to intermediate soil. compute degrees of freedom using the conservative method. interval: to