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Viewing 9 posts - 1 through 9 (of 9 total)
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• #52987

Shaz
Member

hi…can someone help me with these questions….i really dont understand what has to be done.!:(
1) The Academy of Orthopedic Surgeons states that 35% of women wear shoes that are too small for their feet. A researcher wants to be 98% confident that this proportion is within 0.05 of the true proportion. How large a sample is necessary?

2) The National Broomball League claims to have a balanced league; that is, for any given game each team has an equal chance of winning or losing with no ties. Assuming the claim is true, what is the approximate probability that a given team will lose more than 56 games out of the 100 played?

thankss!!

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#187211

Robert Butler
Participant

You picked a particularly bad time to post this to this forum.  Several others have posted homework like this and suffered a major pile on. There’s a good chance you will get chewed out a told to open your book and do some reading.
In the off chance that you have tried and just don’t know what you are looking for I’ll give you the following hint:
Both of your situations are asking a question about one of two possibilities – what is the name of the distribution one uses when there are only two possibilities?
If you can answer this you should be able to look at you statistics text book and find the section (in most modern books I’ve examined this is more likely to be a chapter) devoted to this distribution.  One of the things you will find is in that chapter is the expression for computing a given probability of successes and failures for a fixed number of tests.  This will allow you to answer question #2.  Once you have #2 you should be able to read further in the same chapter and find the methods needed to answer #1.

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#187212

Darth
Participant

Robert, apparently you haven’t read the recent threads either or you are just a big ole softy. Hope you found a trailer hitch this hear and plan to join us at the Conference in Feb.

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#187213

Shaz
Member

a binomial distribution…its a multiple choice
question…i tried doing it but i dont get the answers
listed so i did not know what i was doing wrong!!i
don’t want people to put down the answers for me…but
to just guide me through solving it..because i tried
several ways and failed!

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#187214

Robert Butler
Participant

Ok, so if it’s a binomial distribution then in question #2 what are the probabilities of success and the probabilities of failure?  What’s the total sample size and what’s the number of failures and successes for that particular problem?  If you can figure those out then, if your textbook is any good at all it should have the expression you need to use to compute the probability of losing more than 56 games.

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#187215

Shaz
Member

the probability of success is 0.5 and the probability of failure is 0.5 too. sample size is 100…

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#187217

Robert Butler
Participant

Ok, and what about the rest – the success/ failure count?  Take these and the other numbers you have identified, find the expression for probability in the chapter, run the calculations, and you should have your answer.
Another hint – if you don’t happen to have the ability to compute factorials you will have to run a Google search and find a table of log10 values for factorials up to 100! and then run your calculations in log units and back transform at the end.

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#187223

StuW
Member

It is also difficult to know exactly what has been taught to students when these questions arise.  In this case, do they know the Normal approximation to the binomial distribution for larger sample sizes?   In that instance, the solution becomes rather quick by stadardizing the 56% value (or 44%, value if considering wins) and then finding the area on the Normal curve beyond that value.
Shaz, consider that another hint as all you need is to substitute the appropriate value for sigma in the standardization formula and then use the Normal curve to find the answer.

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#187224

Robert Butler
Participant

That’s a good point StuW.  I made the assumption that Shaz’s book/handout was built like most of the intro books I have – first the general expression for the binomial with the normal approximation showing up in later chapters.  Between the hints you and I have given the poster should be able to figure it out.

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