2B. (a) An exponential distribution has probability density function f(x) = ¹²e-x/a, x≥0. a Show that the mean of the distribution is a and the variance is a². (b) A machine contains two belt drives, of different lengths. These have times to failure which are exponentially distributed, with mean times a and 2a. The machine will stop if either belt fails, and the failures of the belts are independent. Show that the chance that the machine is still operating after a time a from the start is e 32

A First Course in Probability (10th Edition)
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ISBN:9780134753119
Author:Sheldon Ross
Publisher:Sheldon Ross
Chapter1: Combinatorial Analysis
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Problem 1.1P: a. How many different 7-place license plates are possible if the first 2 places are for letters and...
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2B.
(a) An exponential distribution has probability density function
ƒ(x) = ¹²e-x/a, x ≥0.
α
Show that the mean of the distribution is a and the variance is a².
(b) A machine contains two belt drives, of different lengths. These have times to failure which
are exponentially distributed, with mean times a and 2a. The machine will stop if either belt
fails, and the failures of the belts are independent. Show that the chance that the machine is
still operating after a time a from the start is e 32
Transcribed Image Text:2B. (a) An exponential distribution has probability density function ƒ(x) = ¹²e-x/a, x ≥0. α Show that the mean of the distribution is a and the variance is a². (b) A machine contains two belt drives, of different lengths. These have times to failure which are exponentially distributed, with mean times a and 2a. The machine will stop if either belt fails, and the failures of the belts are independent. Show that the chance that the machine is still operating after a time a from the start is e 32
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