# Thread: Normal distribution problem

1. ## Normal distribution problem

#1
Suppose that the time spent each month on a mobile-phone by a subscriber with a particular profile is normally distributed with a mean of 175 minutes and a standard
deviation of 45 minutes.
A mobile-phone operator offers the subscriber a monthly flat rate plan:

• 90 minutes’ use or less costs 35 dollars

• between 90 minutes’ and 240 minutes’ use costs 60 dollars

• more than 240 minutes’ use costs 75 dollars.

Question 1:
Assuming that the subscriber’s use of the phone does not change, calculate the mean and standard deviation of the subscriber’s monthly charges.

Question 2:
Why is the assumption that the use will not change unrealistic?

2. ## Re: Normal distribution problem

Originally Posted by hsetima
#1
Suppose that the time spent each month on a mobile-phone by a subscriber with a particular profile is normally distributed with a mean of 175 minutes and a standard
deviation of 45 minutes.
A mobile-phone operator offers the subscriber a monthly flat rate plan:
• 90 minutes’ use or less costs \$35 • between 90 minutes’ and 240 minutes’ use costs \$60
• more than 240 minutes’ use costs \\$75.

Question 1:
Assuming that the subscriber’s use of the phone does not change, calculate the mean and standard deviation of the subscriber’s monthly charges.
Question 2:
Why is the assumption that the use will not change unrealistic?
Please show what you have done and tell us what you do not understand.