# Reliability and Risk Division

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## TECH SPOT: SAMPLE CRE QUESTIONS (Part 21)

#### By Tim Gaens posted 06/05/23 04:12 PM

1. A system made up of 5 series components has a design reliability of .96. Subsequently, 4 of the components have reliabilities apportioned to them of 0.992, 0.991, 0.994, and 0.992. What should the reliability apportionment for the 5th subsystem be?
A. 0.970
B. 0.969
C. 0.990
D. 0.992

2. Which process has as its principal parts:

A. Predicting reliability.

B. Design review.

C. Defining the program plan.

D. Demonstrating the reliability.

3. 10 units have entered the field in the last two months with current times: 25, 33, 40, 45, 50, 60, 64, 75, 80, 99. Failure distribution β=3.02, η=88
What is the expected number of units predicted to fail over the next 5 months?
A, 5.44

B. 6.44

C. 7.44

D. 8.44

4. The reliability for a Weibull distribution with β=2) is:

Find the MTTF in terms of η

A,

B.

C.

D.

5. Suppose that two identical units are placed in active parallel. Each has a Weibull distribution with known 𝜂 and β > 1. Determine the system reliability.

A.

B.

C.

D.

6. Root cause analysis provides a common sense approach to evaluating a problem.
Align the following action steps in proper
sequence from start to finish.
I. . Describe problem conditions.
II. . Develop possible problem causes.
III. . Collect facts and determine relationships.
IV. . Validate the true problem causes.
V. . Define the problem statement.

A. I, V, IV, II, III

B. V, I, III, II, IV

C. I, V, III, IV, II

D. V, III, I, IV, II

7. The Arrhenius model is used to predict part reliability.
Which of the following are valid Arrhenius model statements ?
I. . The rate of chemical reaction doubles for every 10°F rise.
II. . It is useful for all accelerated testing plans.
III. . It is useful for significant thermal stresses.
IV.. It provides a relationship of failure to temperature.

A. I and II only

B. II and III only

C. III and IV only

D. I, III and IV only

8. The rated breaking strength of a suspension bridge cable is 150,000 pounds. An example using this cable in a derated condition is which of the following ?

A. The cable in a 75,000 pound maximum stress application
B. The cable in a 150,000 pound maximum stress application
C. The cable in a 225,000 pound maximum stress application
D. The cable as a parallel component.

9. A home computer manufacturer determines that his machine has a constant failure rate of λ = 0.4 per year in normal use. For how long should the warranty be set if no more than 5% of the computers are to be returned to the manufacturer for repair?

A. ~96 days

B. ~47 days

C. ~10 days

D. ~37 days

10. The reliability of a cutting tool is given by

where t is in hours. What is the MTTF?

A. 1.67 hrs

B. 3.33 hr

C. 6.66 hr

D. 10 hr.