Question

The time spent watching TV per week by middle-school students has a normal distribution with mean 20.5 hours and standard deviation 5.5 hours.

(a) Find the percent who watch less than 25 hours per week

(b) Find the percent who watch over 30 hours per week

Answer 1

Suppose, random variable X denotes time spent (in hours) watching TV per week by middle-school students.

(a)

Corresponding probability is given by

[Using R-code 'pnorm(0.8181818)']

Hence, 79.34% students watch TV less than 25 hours per week.

(b)

Corresponding probability is given by

   [Using R-code '1-pnorm(1.727273)']

Hence, 4.21% students watch TV over 30 hours per week.