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

Question

Quizplus · Accepted Answer

To find the sample size needed, we can use the formula:

n = (z*s / E)^2

where z is the z-score corresponding to the desired confidence level (80% = 1.28), s is the population standard deviation (150 mg), and E is the margin of error (10 mg).

Plugging in these values, we get:

n = (1.28*150 / 10)^2
n = 369

Therefore, the manufacturer needs to weigh at least 369 nickels to obtain an average accurate to within 10 milligrams with 80% confidence. So the correct choice is (B).

A Study of Nickels Showed That the The Standard Deviation