Question 1

Waygate's residential internet modem works well but is sensitive to power-line fluctuations.On average, this product hangs up and needs resetting every 200 hours.On average about 45 minutes is needed to reset this product.What is this product's availability?

A)Not in excess of .75
B)In excess of .75 but not in excess of .8
C)In excess of .8 but not in excess of .9
D)In excess of .9 but not in excess of .95
E)In excess of .95

E

Accepted Answer

E

Question 2

A system consists of two components, each of which must activate if the system is to activate.One component has a reliability of .99.The other has a reliability of .95.The components are independent of one another with respect to reliability.What is the overall system reliability?

A).99
B).95
C).94
D).90
E)Cannot be determined with this information.

C

Accepted Answer

The overall system reliability can be found by multiplying the reliabilities of each component: .99 x .95 = .9405 or 94.05%. Therefore, the closest answer choice is C, with a reliability of 94%.

Question 3

A system consists of two components, each of which must activate if the system is to activate.One component has a reliability of .99.The other has a reliability of .95.What is the overall system reliability?

A).99
B).95
C).94
D).90
E)Cannot be determined with this information.

E

Accepted Answer

E

Question 4

Redundancy is often more cost-effective than increasing individual component reliability.

Accepted Answer

Redundancy allows for multiple components to be used instead of increasing the reliability of just one component. This can often be a more cost-effective solution as the cost of duplicating a component is often less than the cost of increasing the reliability of a single component. Additionally, redundancy also provides added benefits such as improved system availability and decreased downtime in the event of a failure.

Question 5

An electrical appliance will not work unless component QK does.Component QK's reliability is 0.95.Every other part of the appliance is 100% reliable.What would the reliability of the appliance be if a backup QK were added?

A).95
B).9975
C).9025
D).9205
E).9795

Accepted Answer

The appliance will only work if component QK works, which has a reliability of 0.95. The probability of QK failing is 0.05. If a backup QK is added, the reliability of the appliance would be the probability of both components not failing, which would be the product of their individual reliabilities. 
Probability of first QK working = 0.95 
Probability of backup QK working = 0.95 
Probability of both QKs working = 0.95 x 0.95 = 0.9025 
Probability of both QKs failing = 0.05 x 0.05 = 0.0025 
Probability of at least one QK working = 1 - probability of both failing = 1 - 0.0025 = 0.9975 
Therefore, the reliability of the appliance with a backup QK would be 0.9975 or 99.75%.

Question 6

Reliability is the probability that a product or system will function when activated.

Accepted Answer

Reliability is indeed defined as the probability that a product or system will function as intended when activated.

Question 7

Product reliability involves both short-term and long-term perspectives.

Accepted Answer

Product reliability refers to the ability of a product to perform its stated function without failure over a certain period of time, and it is important to consider both short-term and long-term perspectives to ensure customer satisfaction and sustained success in the market.

Question 8

If a system depends on two sub-systems functioning when activated, the reliability of that system is equal to the lower reliability of the two sub-systems.

Accepted Answer

The reliability of a system that depends on two sub-systems functioning is the product of the reliabilities of the two sub-systems, not the lower reliability of the two.

Question 9

The time between failures for an electrical appliance is exponentially distributed with a mean of 25 months.What is the probability that the next failure won't occur before 30 months have elapsed?&#10;A)Not in excess of .2&#10;B)In excess of .2 but not in excess of .3&#10;C)In excess of .3 but not in excess of .4&#10;D)In excess of .4 but not in excess of .6&#10;E)In excess of .6

Accepted Answer

Given that the time between failures follows an exponential distribution with a mean of 25 months. We know that for an exponential distribution, the probability of failure in the next 30 months can be calculated as:

P(X > 30) = e^(-30/25) = 0.4493

Therefore, the probability that the next failure won't occur before 30 months have elapsed is:

P(X <= 30) = 1 - P(X > 30) = 1 - 0.4493 = 0.5507

This probability is in excess of 0.3 but not in excess of 0.4, so the best choice is C.

Question 10

Availability cannot be increased without improving the time between breakdowns.

Accepted Answer

Availability can also be increased by reducing the time it takes to repair or restore a system after a breakdown, not just by improving the time between breakdowns.

Deck 20: Extension 4: Reliability