## TECH SPOT: SAMPLE CRE QUESTIONS (Part 23)

1. Compared to quality, reliability engineering is more concerned with :

I. . Failure rate over time.

II. . Manufacturing errors.

III. . Defective rate at a point in time.

IV. . Product design.

A. I and II only

B. II and III only

C. I, II, III and IV

**D. I and IV only**

** **

2. The components in the system below are exponentially distributed with the indicated failure rates. Develop an expression for the reliability of the system. What is the system reliability at time = 100 hours ?

A. 0.008

**B. 0.4493**

C. 0.8

D. 0.334

3 . A home computer has two 3.5 inch disk drives. What is the probability of the computer operating successfully (with at least one disk drive) for 1000 hours. Assume the following estimated reliability values of the components. (where R(t) = e – λt):

**A.0.9426**

B. 0.9173

C. 0.9373

D. 0.9833

4. The Space shuttle had 12 O-rings*. If any of the 12 rings fail, the shuttle would explode. If the probability of a single O-ring failing is .01, what’s the probability of an explosion? Assume the rings operate independently.

A. 0.1047

**B. 0.1136**

C. 0.0135

D. < 0.001

5. A supplier of parts claims it has a manufacturing process in which 90% of parts are defect free. To check this theory, a customer randomly samples 25 parts and finds seven that are defective.

If the supplier’s claim is true, what is the probability that 7 or more of the 25 sampled parts are defective? (Assume Binomial)

A. 0.9977

B. 0.9905

**C. 0.009476**

D. 0.002261

6: On an interplanetary probe, the system has five synchronous computers that analyze all other systems and compare the results with each other. For a launch to take place, four out of five computers must agree on the system parameters. If all agree, the launch takes place. If one computer fails and four agree, the fifth computer is ignored and the launch occurs. If two computers fail to agree, the launch is scrubbed. The reliability of a computer is 0.995. What is the probability of a successful launch?

A. 0.9985

B. 0.9975

**C. 0.99975**

D. 0.991

7: Ideally for a FRACAS to be effective, how many failures should be allowed to pass before corrective action is to be undertaken ?

**A. First occurrence of a failure mode.**

B. Second occurrence of a failure mode.

C. Third occurrence of a failure mode.

D. Fourth occurrence of a failure mode.

8. A life test with type II censoring is performed on 50 servomechanisms that are thought to have a constant failure rate. The test is terminated after the twentieth failure. The times to failure (in months) are as follows:

Assuming the failure data follows an exponential, what are the 90% confidence intervals on the MTTF?

A. 2.85 months ≤MTTF≤15.59 months,

B. 1.9 months≤MTTF≤16.59 months,

C. 0.5 months ≤MTTF≤ 1659 months,

**D. 5.9months≤MTTF≤12.59 months**

9. When prioritizing actions to be taken in an FMEA, which of the following priority rankings should be considered first?

A. Overall RPN (Risk Priority Number)

**B. Highest severity ranking**

C. Highest occurrence ranking

D. Highest severity times occurrence ranking

10. Complete the following partial design FMEA and select the first next step.

A. Provide an alternate means to power on the unit to lower the detection score of line 1

B. Provide an alternate means to power down the unit to lower the occurrence score of line 2

C. Provide an alternate location of the switch to lower the occurrence score of line 3**D. Provide a safety switch that bypasses the power switch to reduce the severity score of line 2 &3**