Q 21

A study of nickels showed that the the standard deviation of the weight of nickels is 150 milligrams. A coin counter manufacturer wishes to find the 80% confidence interval for the average weight of a nickel. How many nickels does he need to weigh to obtain an average accurate to within 10 milligrams?
A) 225
B) 369
C) 613
D) 159

Q 22

A previous analysis of paper boxes showed that the the standard deviation of their lengths is 15 millimeters. A packer wishes to find the 90% confidence interval for the average length of a box. How many boxes does he need to measure to be accurate within 3 millimeters?
A) 25
B) 97
C) 69
D) 41

Q 23

A study of elephants is conducted to determine the average weight of a certain subspecies of elephants. The standard deviation for the population is 1500 pounds. At a 95% level, how many elephants need to be weighed so the average weight will be accurate to within 250 pounds?
A) 139
B) 165
C) 196
D) 324