A sample of fifth-grade classes was studied in the journal article "Predicting Feelings of School Safety for Lower, Middle, and Upper School Students" (Applied Psychology in Criminal Justice, Vol. 7, Issue 2, pp. 59-76) by R. Bachman et al. One of the variables collected was the class size in terms of student-to-faculty ratio. The student-to-faculty ratios of the 81 fifth grade classes sampled have a mean of 15.83 and a standard deviation of 1.74.

(Round answers to 2 decimal places)

Assuming the variable "student-to-faculty ratios" has a normal distribution, answer the following questions.

How many fifth grade classes contain "student-to-faculty ratios" from 10.61 to 21.05?