In: Statistics and Probability
Use the central limit theorem to solve the problem.
Quiz scores for Grammer 222 class are normally distributed with a mean of 60.5 and a standard deviation of 10.5.
1. If a student is chosen, find the probability that this student's score is at least 70.2?
2. If a sample of 22 students is randomly selected, find the probability that their mean score is at least 70.2?
Solution :
Given that ,
1) P(x
70.2) = 1 - P(x  
70.2)
= 1 - P[(x - 
) / 
(70.2 - 60.5) / 10.5]
= 1 -  P(z 
 0.92)
= 1 - 0.8212
= 0.1788
2) 
= 60.5

= 
 / 
n = 10.5 / 
22 = 2.24
P(
70.2) = 1 - P(
70.2)
= 1 - P[(
- 
) / 

(70.2 - 60.5) / 2.24]
= 1 - P(z 
 4.33)   
= 1 - 1
= 0