Question 1

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?
A) 0.95
B) 0.9975
C) 0.9025
D) 0.9205
E) 0.9795

Accepted Answer

The reliability of the appliance with only one QK is 0.95. The failure rate of QK is 0.05, so the probability that it will fail is 0.05. The probability that both QKs will fail is 0.05 x 0.05 = 0.0025. Therefore, the probability that at least one QK will be working is 1 - 0.0025 = 0.9975. This means that adding a backup QK would increase the reliability of the appliance to 0.9975.

Question 2

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

Accepted Answer

This is a correct definition of reliability.

Question 3

One way to increase overall reliability of a system is to add parts that increase redundancy in the system.

Accepted Answer

Adding redundant parts means having backup or duplicate components in case one fails, which increases the system's reliability by providing a fail-safe mechanism.

Question 4

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 5

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) 0.99
B) 0.95
C) 0.94
D) 0.9
E) Cannot be determined with this information.

Accepted Answer

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

Question 6

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

Accepted Answer

Product reliability is important not only in the short term (i.e. immediate functionality and use), but also in the long term (i.e. durability and continued performance over time). A product that may work well initially but fails quickly may have a lower level of overall reliability than a product that works consistently over a longer period of time.

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. The components are independent of one another with respect to reliability. What is the overall system reliability?
A) 0.99
B) 0.95
C) 0.94
D) 0.9
E) Cannot be determined with this information.

Accepted Answer

The overall system reliability can be calculated using the formula:
Overall reliability = 1 - (1 - reliability of component 1) x (1 - reliability of component 2)
Substituting the given values, we get:
Overall reliability = 1 - (1 - 0.99) x (1 - 0.95)
Overall reliability = 1 - (0.01 x 0.05)
Overall reliability = 0.9995
Therefore, the overall system reliability is 0.94 (rounded to two decimal places).

Question 8

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)?
A) not more than 200 hours
B) more than 200 hours but not more than 400 hours
C) more than 400 hours but not more than 600 hours
D) more than 600 hours but not more than 800 hours
E) more than 800 hours

Accepted Answer

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

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 will not occur before 30 months have elapsed?
A) not in excess of .2
B) in excess of .2 but not in excess of .3
C) in excess of .3 but not in excess of .4
D) in excess of .4 but not in excess of .6
E) in excess of .6

Accepted Answer

The probability that the next failure will not occur before 30 months have elapsed can be calculated as:
P(X > 30) = e^(-30/25) = 0.449
This means that there is a 44.9% chance that the appliance will not fail before 30 months have elapsed. 
Since this probability is in excess of .3 but not in excess of .4, the best choice is option C.

Question 10

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 __________.
A) increasing; reliability
B) reducing; time required for repair
C) reducing; reliability
D) reducing; reparability
E) increasing; time required for repair

Accepted Answer

By reducing the time required for repair, the product can be quickly fixed when it fails, maintaining its availability even if the average amount of time it goes without failing decreases. Increasing reliability or increasing time required for repair would not necessarily maintain the same level of availability. Reducing reparability or reliability would likely decrease availability.

Question 11

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

Accepted Answer

Availability = (Uptime)/(Uptime + Downtime) = (200 hours)/(200 hours + 45 minutes) = (200 hours)/(200 hours + 0.75 hours) = 0.9962 = 99.62%

Question 12

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

If a system depends on two subsystems, the overall reliability is determined by the probability of both subsystems functioning at the same time. Therefore, the overall reliability is lower than that of the less reliable subsystem. This is known as the "AND" configuration of subsystems. In contrast, if the system depends on either one of the subsystems functioning when activated, the overall reliability would be higher and equal to that of the more reliable subsystem. This is known as the "OR" configuration of subsystems.

Quiz 4: RELIABILITY – Static

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?

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

One way to increase overall reliability of a system is to add parts that increase redundancy in the system.

Availability cannot be increased without improving the time between breakdowns.

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?

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

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?

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?

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 .

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?

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