An Epson inkjet printer ad advertises that the black ink car

An Epson inkjet printer ad advertises that the black ink cartridge will provide enough ink for an average of 245 pages. Assume that this claim is accurate and that the standard deviation for this population is 15 pages. A random sample of 33 customers was surveyed about the number of pages they were able to print with their black ink cartridges. What the probability that the sample mean will be 246 pages or less?

0.6480

0.8729

0.3520

0.1093

Solution

We first get the z score for the critical value. As z = (x - u) sqrt(n) / s, then as          
          
x = critical value =    246      
u = mean =    245      
n = sample size =    33      
s = standard deviation =    15      
          
Thus,          
          
z = (x - u) * sqrt(n) / s =    0.38      
          
Thus, using a table/technology, the left tailed area of this is          
          
P(z <   0.38   ) =    0.6480 [ANSWER, A]