The typical college freshman spends an average of u150 minut

The typical college freshman spends an average of u=150 minutes per day with a standard deviation of 50 minutes on social media. The distribution of time on social media is known to be Normal. The upper quartile is:

a. 116.27

b. 0.25

c. 0.75

d. 183.72

Solution

P ( Z < x ) = 0.75
Value of z to the cumulative probability of 0.75 from normal table is 0.674
P( x-u/s.d < x - 150/50 ) = 0.75
That is, ( x - 150/50 ) = 0.67
--> x = 0.67 * 50 + 150 = 183.72