A small company uses three computers to trade on the New York Stock Exchange (NY
ID: 3044768 • Letter: A
Question
A small company uses three computers to trade on the New York Stock
Exchange (NYSE). The chance of a computer failing in a day is 0.8%, and the computers
fail independently. Computers are repaired in the evening, and each day is an independent
trial. Let us define two events as follows:
A: a specific computer fails on a day
B: all three computers fail on the same day
3. What is the mean number of days until a specific computer fails?
4. What is the mean number of days until all three computers fail on the same day?
Explanation / Answer
Solution:
Probability of event A occurs on a day
3.The mean number of days until a specific computer fails
Therefore
= E[X] = 1/p
= 1/0.8 = 1.25
4.Probability of event B occurs on the same day = P( all failes)
The mean number of days until all three computer fail in the same day is
= E[Y] = 1/(0.8)^3
= 1.953