Chapter 04S – Reliability
1. Reliability is the probability that a product or system will function when activated.
2. 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.
3. Redundancy is often more cost-effective than increasing individual component reliability.
Chapter 04S – Reliability
4. Availability cannot be increased without improving the time between breakdowns.
5. Product reliability involves both short-term and long-term perspectives.
Chapter 04S – Reliability
6. 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?
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?
Chapter 04S – Reliability
4S-4
8. 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?
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?
Chapter 04S – Reliability
10. 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?