which of the two classes had more scores of 90 or better? Why?

Question

tow classes, each with 100 students, took an examination with a maximum possible score of 100. In the first class the mean score was 75, and the standard deviation was 5. In the second class, the mean score was 70, and the standard deviation was 15.

Answer 1

1st class:

Prob ( X>=90) =  1 - Prob(X < 90)  = ` 1 - Prob( z < (90-75)/5 ) = 1 - Prob ( z < 3) = 1 - 0.9987 = 0.0013 = 0.13%

 

2nd class, using the same calculations as before with different z-score:

  1 - Prob ( z < (90-70)/15) )= 1 - Prob ( z < 4/3) = 1 -  0.9082 = .0918 = 9.18%

 

The second class has more A's because the probability is higher

 

 

Answer 2

first class

z = (90 - 75) / 5

z = 25 / 5

z = 3

 

second class

z = (90 - 70) /15

z = 20 / 15

z = 1.333...

 

What is the answer?