# Statistical Consideration of Design - Mechanical Engineering (MCQ) questions and answers

1)   What is the standard deviation of clearance population for the diameter of shaft and hole assembly specified below?
Shaft diameter = 30 ± 0.15
Hole diameter = 30.5 ± 0.25

a. 0.097 mm
b. 0.059 mm
c. 0.036 mm
d. 0.390 mm
 Answer  Explanation ANSWER: 0.097 mm Explanation: No explanation is available for this question!

2)   What causes infant mortality in mechanical equipments?

a. Design errors
b. Manufacturing defects
c. Installation defects
d. All of the above
 Answer  Explanation ANSWER: All of the above Explanation: No explanation is available for this question!

3)   A plain carbon steel has mean yield strength of 300 N/mm2 and standard deviation of 50 N/mm2. What is the mean and standard deviation of margin of safety, if mean tensile stress of 250 N/mm2 and standard deviation of 65 N/mm2 acts on it?

a. 23.45 N/mm2, 50 N/mm2
b. 50 N/mm2, 82 N/mm2
c. 82 N/mm2, 7.07 N/mm2
d. 7.07 N/mm2, 50 N/mm2
 Answer  Explanation ANSWER: 50 N/mm2, 82 N/mm2 Explanation: No explanation is available for this question!

4)   What is meant by mean time to failure (MTTF)?

a. Mean time between two successive failure components
b. Maximum time between two successive failure components
c. Sum of survival time for number of components divided by number of failures
d. Sum of number of failures divided by survival time for number of components
 Answer  Explanation ANSWER: Sum of survival time for number of components divided by number of failures Explanation: No explanation is available for this question!

5)   If a relief valve has reliability of 0.989, how many failures are expected in testing 1000 such relief valves?

a. 111
b. 100
c. 10
d. 11
 Answer  Explanation ANSWER: 11 Explanation: No explanation is available for this question!

6)   Failure rate for safety valve working for 400 hours is 3 x 10–6 failures/hour. What is the reliability of safety valve?

a. 0.998
b. 0.989
c. 0.888
d. 0.899
 Answer  Explanation ANSWER: 0.998 Explanation: No explanation is available for this question!

7)   What is meant by hazard rate?

a. Number of failures per unit time per number of items when exposed for same time
b. Probability of test specimen fails between time t1 and t1 + dt1 which survives for time t1
c. Both a. and b.
d. None of the above
 Answer  Explanation ANSWER: Both a. and b. Explanation: No explanation is available for this question!

8)   Which of the following curves have the mean value equal to zero in the graph of frequency vs random variable?

a. Normal distribution curve
b. Standard normal distribution curve
c. Both a. and b.
d. None of the above
 Answer  Explanation ANSWER: Standard normal distribution curve Explanation: No explanation is available for this question!

9)   What is the relation between standard deviation(σ) and arithmetic mean (μ) to determine coefficient of variation (C)?

a. C = σ + μ
b. C = σ – μ
c. C = σ / μ
d. C = σ x μ
 Answer  Explanation ANSWER: C = σ / μ Explanation: No explanation is available for this question!

10)   Assignable causes are caused due to changes in _________

a. manufacturing process
b. material
c. inspection process
d. all of the above
 Answer  Explanation ANSWER: all of the above Explanation: No explanation is available for this question!