1 point A student takes a 20question exam The time that he n

(1 point) A student takes a 20-question exam. The time that he needs to solve each problem is randomly distributed with mean of 6 minutes and standard deviation of 1.1 minute. What is the probability that he finishes the exam in less than115 minutes? 6. A) 0.15 B) 0.50 C) 0.75 D) 0.85

Solution

We first get the z score for the critical value. As z = (x - u) sqrt(n) / s, then as          
          
x = critical value = 115/20 =   5.75      
u = mean =    6      
n = sample size =    20      
s = standard deviation =    1.1      
          
Thus,          
          
z = (x - u) * sqrt(n) / s =    -1.016394535      
          
Thus, using a table/technology, the left tailed area of this is          
          
P(z <   -1.016394535   ) =    0.154720773 = 0.15 [answer, A]