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# Stats practise help!!! watch

1. Hey im trying to do some stats practise for summer and need help going through this question im trying to do:

The diameter of cable can be assumed to have a normal distribution with mean 0.9cm and standard deviation 0.015cm

*the cable is considered defective if the diameter differs frm the mean by more than 0.025cm. Calculate the probability that a randomly selected cable is defective?

* the company incurs a penalty of £20 for every defective cable and each cable whose diamter differs from the mean by more than 0.04cm incurs a further penalty of £10. calculate expected penalty per cable
2. Remember for the first one than it can be too fat or too thin, and so the probability you want is

For the next part, construct a table for the possiblities: £0, £20, £30, and calculate the probability for each. The most important thing is that the probability of £20 is not as simple as normal.

After doing this, use expectation theory to find the expected penalty, where . The notation meaning is the probability of penalty occurring.
3. (Original post by coffeym)
Remember for the first one than it can be too fat or too thin, and so the probability you want is

For the next part, construct a table for the possiblities: £0, £20, £30, and calculate the probability for each. The most important thing is that the probability of £20 is not as simple as normal.

After doing this, use expectation theory to find the expected penalty, where . The notation meaning is the probability of penalty occurring.
ok i really dont get the first part
4. (Original post by Amiro)
ok i really dont get the first part
P(T < 0.875) + P(T > 0.925). Both of which are the same since the distribution is symmetrical.
5. (Original post by generalebriety)
P(T < 0.875) + P(T > 0.925). Both of which are the same since the distribution is symmetrical.
do i square root standard deviation to get vairance
6. No, variance = (standard deviation

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