Question

Nationally, the average class size in K-12 classrooms is 23 students with a standard deviation of 2.5.

A. What proportion of classrooms has less than 25 students?

B. What is the class size to be considered in the bottom fifth percentile?

Answer 1

Average = u = 23

Standard deviation = s = 2.5

A. P( X < 25 )

Z = ( X - u ) /s

= ( 25 - 23 )/2.5

= 0.8

P( Z < 0.8 ) = 0.7881 = 78.81%

b. Values below 18.87