(A.) You are responsible for quickly fixing your company's computer system when it crashes. You know that there are three possible sources of errors in the system: the disk drive, the memory and the operating system.

From an analysis of historical data, you find that 50% of the errors are disk errors, 30% are memory errors and the remaining errors are operating system errors.

From component performance standards, you know that when a disk error occurs, the probability that the computer crashes is 60%, when a memory error occurs, the probability that the computer crashes is 70%, and when an operating system error occurs, the probability that the computer crashes is 40%.

The company computer has just crashed! You need to quickly decide which component (disk drive, memory or operating system) is the best component to look at first in your attempt to get the computer back on line.

Calculate all of the relevant __conditional__ probabilities. Then, using this information, which component should you probably investigate first?

**(8.) - **A contractor estimates the probabilities for the number of days required to complete a certain type of construction project as follows:

**Time (days)**

1

2

3

4

5

**Probability**

0.05

0.20

0.35

0.30

0.10

(a) Calculate the expected time to complete the project. - (3 Points)

(b) Calculate the standard deviation of the time to complete the project. - (4 Points)

The contractor's project cost is composed of two parts: a fixed cost of $20,000 plus $2,000 for each day required to complete the project.

(c) Calculate the expected value and standard deviation of total project cost. - (5 Points)