Television viewing reached a new high when the global information and measurement company reported a mean daily viewing time of hours per household. Use a normal probability distribution with a standard deviation of hours to answer the following questions about daily television viewing per household.
a. what is the probability that a household views television between 6 and 8 hours a day (to 4 decimals)?
b. How many hours of television viewing must a household have in order to be in the top 5% of all television viewing households (to 2 decimals)?
c. What is the probability that a household views television more than 5 hours a day (to 4 decimals)?

Television viewing reached a new high when the global information and measurement company reported a mean daily viewing time of 8.35 hours per household. Use a normal probability distribution with a standard deviation of 2.5 hours to answer the following questions about daily television viewing per household.

(a.) what is the probability that a household views television between 6 and 8 hours a day (to 4 decimals)?

(b.) How many hours of television viewing must a household have in order to be in the top 5% of all television viewing households (to 2 decimals)?

(c.) What is the probability that a household views television more than 5 hours a day (to 4 decimals)?

Solution:

Let x be the random variable representing the television viewing times per household. Since it is normally distributed and the population mean and population standard deviation are known, we would apply the formula,

z = (x - µ)/σ

Where

x = sample mean

µ = population mean

σ = standard deviation

From the information given,

µ = 8.35

σ = 2.5

a) the probability that a household views television between 6 and 8 hours a day is expressed as

P(6 ≤ x ≤ 8)

For x = 6,

z = (6 - 8.35)/2.5 = - 0.94

Looking at the normal distribution table, the probability corresponding to the z score is 0.1736

For x = 8

z = (8 - 8.35)/2.5 = - 0.14

Looking at the normal distribution table, the probability corresponding to the z score is 0.4443

Therefore,

P(6 ≤ x ≤ 8) = 0.4443 - 0.1736 = 0.2707

b) the top 5% means greater than 95%. It means that the sample mean is greater than the population mean and the z score is positive. The corresponding z score from the normal distribution table is 1.645. Therefore,

(x - 8.35)/2.5 = 1.645

Cross multiplying, it becomes

x - 8.35 = 2.5 × 1.645 = 4.11

x = 4.11 + 8.35 = 12.46

c) the probability that a household views television more than 5 hours a day is expressed as

P(x > 5) = 1 - P(x ≤ 5)

For x = 5

z = (5 - 8.35)/2.5 = - 1.34

Looking at the normal distribution table, the probability corresponding to the z score is 0.0901

Therefore,

P(x > 5) = 1 - 0.0901 = 0.9099