Math Is Fun Forum

pw

Member

Registered: 2006-12-05

Posts: 3

Stats help needed!

Any help much appreciated!

Q1. In the mass production of jars of Goldtaste coffee, the probability that a jar of coffee is rejected because it is underweight is 5%. If random samples of 10 jars are selected for inspection, find the probability that in any such sample:

  i) three jars are rejected.
  ii) At most three jars are rejected.

If two random samples of 10 jars are selected at the same time:

iii) Find the probability that no jars are rejected in either sample.
  iv) find the probability that one jar is rejected

Suppose that p = Probability that out of a random sample of n jars, there is at least 1 acceptable jar. If P > 0.09999992, show that 0.0000008 > (0.05)^n and hence find the min value of n.

Q2: A machine produces components in batches of 20000. At the beginning of production, the machine is set to produce the required mean length of components at 30mm and then be set to give any of 3 standard deviations:

Setting 1   0.12 mm - cost of this setting S.D. = £850
Setting 2   0.15 mm - cost of setting this standard deviation = £550
Setting 3   0.18 mm - Cost of setting this S.D. = £100

Any length produced must lie between 29.65mm and 30.41 mm, otherwise it is classed as defective and costs the company £1. You can assume the length of a component is Normally distributed. Which S.D. should be used if the decision is to be purely based on combined cost of setting the machine and of the defectives?

cheers

Dross

Member

Registered: 2006-08-24

Posts: 325

Re: Stats help needed!

This is the place to come if you enjoy maths - not the place to come if you have some homework questions you cannot be bothered with. Nobody wants to do your homework. The people on this site are, however, quite interested in showing you how to do maths.

Why don't you show us what attempts you've made on these questions? Perhaps you could share any specific difficulties you have (like my difficulty in spelling) - like "how do you start this question" or "is this the right approach - it doesn't seem to go anywhere".

Please, show some attempts at some working, and the people on this site will be glad to answer your queries.

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Bad speling makes me [sic]

Devantè

Real Member

Registered: 2006-07-14

Posts: 6,400

Re: Stats help needed!

'pw', at least try. I can probably tell that you haven't been using Probability Trees. These would help immensely here.

5 questions...'pw', maybe if you look at the first one, you will realise that it isn't actually of immense difficulty.

balls

Guest

Re: Stats help needed!

i like balls:P