Math Help - Probability Problem

1. Probability Problem

A study of Hub Furniture regarding the payment of invoices reveals the time from billing until payment is received follows the normal distribution. The mean time until payment is received is 20 days and the standard deviation is 5 days.

a. What percent of the invoices are paid within 15 days of receipt?

b. What percent of the invoices are paid in more than 28 days?

c. What percent of the invoices are paid in more than 15 days but less than 28 days?

d. The management of Hub Furniture wants to encourage their customers to pay their monthly invoices as soon as possible. Therefore, it announced that a 2 percent reduction in price would be in effect for customers who pay within 7 days of the receipt of the invoice. What percent of customers will earn this discount?

2. Hi

Hi

This whole question is based on you being able to use the normal distributions chart. If you don't know this, this is where you should start.

In general, for any distribution you ask what are the chances that my
random variable X will take a certain value.

You know for a normal distributed variable that it´s 50% chance of getting a value under/over the mean. They say for example that it´s about 68% chance of X taking values between mean minus one std. dev. and mean plus one std. dev.

That is $P(X \leq x) = 0.5 \mbox{ and } P(X > x) = 0.5$

All this you can find for yourself exactly in this table I am talking about.