In a class of 200 students Bills mark corresponded to a zsco

In a class of 200 students, Bill\'s mark corresponded to a z-score of 1 and Tom\'s mark corresponded to a z-score of 2. If the distribution of marks was bell-shaped (‘normal\') than the number of students with a grade between Bill\'s mark and Tom\'s mark is closest to

A. 5 B. 10 C. 20 D. 30

Solution

z1 = lower z score =    1      
z2 = upper z score =     2      
          
Using table/technology, the left tailed areas between these z scores is          
          
P(z < z1) =    0.841344746      
P(z < z2) =    0.977249868      
          
Thus, the area between them, by subtracting these areas, is          
          
P(z1 < z < z2) =    0.135905122      

Hence, we expect 0.135905122*200 = 27.18

Which is closest to

OPTION D: 30 [ANSWER]