Originally Posted by

**amor_vincit_omnia** Hey all. Here's another I can't get.

The life, X in years of a car part had pdf:

f(x)= 3x² / 7³ * e^-(x/7)³ ; 0 < x < infinity

a) probability that this regulator will last at least 7 years?

b) Given that it lasts 7 yrs, conditional prob. that it will last at least another 3.5 yrs?

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So for a, I got the correct answer by saying p(x>=7) = 1-p(x<=7)

And integrating f(x) from 0--->7

The answer is 0.368

Now for b, would I say 1-integral from 7--> 10.5? Cuz' that's what I was thinking, but it didn't work out. Please explain!