Question 1

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.

Question 2

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

Accepted Answer

Product reliability is concerned with the ability of a product to function without failure over a given period of time. Short-term reliability focuses on the immediate performance of the product, while long-term reliability considers how well it will continue to perform over an extended period of time. Therefore, product reliability involves both short-term and long-term perspectives.

Question 3

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

Accepted Answer

Reliability is defined as the probability of a product or system functioning as intended when activated.

Question 4

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 percent reliable. What would the reliability of the appliance be if a backup QK were added?

Accepted Answer

The reliability of the appliance with only one QK component working is 0.95. This means that the probability of the appliance working is 0.95 or 95%.

Now, if a backup QK component is added, the appliance will work if at least one of the QK components works. This is known as a "parallel" system, where the system works if any individual component works.

The reliability of a parallel system with two components can be calculated using the formula:

R(total) = (R(A) + R(B) - R(A) x R(B)),

where R(A) and R(B) are the reliabilities of the two components.

In this case, both components are identical, so we can simplify the formula to:

R(total) = 2R - R^2,

where R is the reliability of each individual component (0.95).

Plugging in the values, we get:

R(total) = 2 x 0.95 - 0.95^2 = 0.9975

Therefore, the reliability of the appliance with a backup QK component is 0.9975 or 99.75%.

The correct answer is B.

Question 5

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?

Accepted Answer

The answer of Waygate's residential Internet modem works well but...

Question 6

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

Accepted Answer

Redundancy involves adding extra components to a system to ensure functionality even if one or more components fail. While this does increase the initial cost of the system, it is often more cost-effective than trying to increase the reliability of each individual component, which can be much more expensive.

Question 7

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?

Accepted Answer

The answer of A system consists of two components, each...

Question 8

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?

Accepted Answer

To calculate the overall system reliability, we can use the formula:

Overall reliability = (reliability of Component 1) * (reliability of Component 2)

Since the components are independent, we can simply multiply their reliabilities.

Overall reliability = 0.99 * 0.95 = 0.9405

Rounding to two decimal places, the overall system reliability is 0.94, which corresponds to choice C).

Question 9

If a system depends on two subsystems functioning when activated, the reliability of that system is equal to that of the less reliable subsystem.

Accepted Answer

The reliability of the system depends on both subsystems functioning, so the overall reliability will be lower than that of either subsystem alone.

Question 10

Suppose a given control unit fails, on average, every 12,000 hours. It takes an average of 900 hours to repair and reboot this unit. The repair/reboot procedures for this unit are being reconfigured. By how much would average repair/reboot time need to be reduced to increase availability by 5 percent (assuming the control unit's average life remains unchanged)?

Accepted Answer

The answer of Suppose a given control unit fails, on...

Question 11

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 will not occur before 30 months have elapsed?

Accepted Answer

The probability that the next failure will not occur before 30 months have elapsed can be calculated using the cumulative distribution function (CDF) of the exponential distribution. 
P(X > 30) = 1 - F(30) = 1 - e^(-30/25) = 0.3935
Therefore, the probability is in excess of 0.3 but not in excess of 0.4, which corresponds to choice C.

Question 12

If the average amount of time a product goes without failing decreased by some amount, that product's availability could nevertheless be maintained at previous levels by __________ its __________.

Accepted Answer

If the average amount of time a product goes without failing decreased, the availability of the product can still be maintained at previous levels by reducing the time required for repair. This means that even though the product is failing more frequently, it can still be repaired quickly enough to maintain its availability. This option is preferred over reducing the reliability or reparability of the product. Increasing the time required for repair would have the opposite effect and decrease the availability of the product. Increasing the reliability may be a solution, but it would likely come at a higher cost and may not be feasible in all scenarios.

Quiz 4: Extension: Reliability