Question

Suppose the mean cost across the country of a 30-day supply of a generic drug is $46.58, with standard deviation $4.84. Find the probability that the mean of a sample of 100 prices of 30-day supplies of this drug will be between $45 and $50.

****YOU MUST SHOW ALL OF YOUR WORK TO DOCUMENT HOW YOU ARRIVED AT THE SOLUTION****

Answer 1

Solution :

Given that,

mean = = $46.58

standard deviation = = $ 4.84

n = 100

=   = $46.58

= / n = 4.84 / 100 = 0.484

P(45 < < 50)  

= P[(45 - 46.58) / 0.484 < ( - ) / < (50 - 46.58) /0.484 )]

= P(-3.26 < Z < 7.07)

= P(Z < 7.07) - P(Z < -3.26)

Using z table,  

= 1 - 0.0006  

= 0.9994