MHB Please help with this question (cumulative distribution function of X)

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The discussion focuses on deriving the cumulative distribution function (CDF) F(x) from the given probability density function (PDF) f(x) = 10/x^2 for x > 10. The participants are tasked with calculating P(X > 20) using the CDF and determining the probability that at least 3 out of 6 devices will last at least 20 hours. Assumptions regarding the independence of device lifetimes are mentioned as crucial for the probability calculations. Additionally, there is a request for clarification on formatting issues in the post, indicating that contributors should provide their progress for better assistance. The thread emphasizes the importance of clear communication and methodical problem-solving in probability theory.
tiffyuyu
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The probability density function of the lifetime of a certain type of electronic device
(measured in hours), X, is given by

f(x) = 10/x^2,
0,
x > 10;
elsewhere.

(a) Find the cumulative distribution function of X, namely F(x) and hence find
P(X > 20).
(b) What is the probability that of 6 such devices, at least 3 will function for at least 20 hours? What assumption did you make?
 
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