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Quiz 4
Due: 3/15/2013
Do not justify your answers to true-false questions.
1. Briefly (in 50 to 100 words) explain two advantages of the bottoms-up approach for
reliability analysis.
2. The figure below shows the performance variable of a component vs. an input
variable. A designer can control the mean value of the input variable but not the type
of its probability density function and its range. It is important for the performance
variable to be nonnegative and have low variability. Which of the two values, A and
B, of the input variable shown in the figure below is better? Justify briefly your
answer.
Performance variable
Probability
density functions
of input variable
0
A
B
Input variable
Unacceptable
performance
3. If variables X and Y are independent, then the mean value of their sum is equal to the
sum of the mean values, and the variance of the sum is the sum of the variances of
these variables. (T-F)
4. In question 3, if variables X and Y are normal, then the sum is also normal. (T-F)
5. Consider the function YX) = X2. The mean value of X is equal to 2. Then the mean
value of Y(X) is exactly equal to 4. (T-F)
6. In the above question, the mean value of Y(X) is approximately equal to 4, and the
approximation is good if the standard deviation of variable X is small. (T-F)