Let X be the time in hours that the battery of a solar calculator functions properly between exposures to light sufficient to recharge it. Suppose the density of X is given by: f(x) = (50/6)x^-3                              2 < x < 10. a) Verify that this is a valid continuous density. b) Calculate the expression for the cumulative distribution function of X and use it to calculate the probability that the charge of a randomly selected solar cell will last at most four hours before it needs to be used. at most four hours before it needs to be recharged. c) Calculate the average time that a battery charge lasts before it needs to be recharged. d) Calculate E[X2] and use its value to determine the variance of X.     please only answer "d".

A First Course in Probability (10th Edition)
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ISBN:9780134753119
Author:Sheldon Ross
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Chapter1: Combinatorial Analysis
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Let X be the time in hours that the battery of a solar calculator functions properly between exposures to light sufficient to recharge it. Suppose the density of X is given by:
f(x) = (50/6)x^-3                              2 < x < 10.
a) Verify that this is a valid continuous density.


b) Calculate the expression for the cumulative distribution function of X and use it to calculate the probability that the charge of a randomly selected solar cell will last at most four hours before it needs to be used.
at most four hours before it needs to be recharged.


c) Calculate the average time that a battery charge lasts before it needs to be recharged.


d) Calculate E[X2] and use its value to determine the variance of X.

 

 

please only answer "d".

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