Quote:
Originally Posted by DanT
Hi Fat Elvis,
The problem involves a discrete distribution that puts 25% probability on each of the integers from 1 to 4. The course materials should have provided you a formula for computing the standard deviation for such a distribution, right? If you were to plot the density of that distribution, you will see that it looks nothing like a normal curve. Instead, the distribution puts the same amount of weight on each of only 4 points. You can compute the standard deviation for the problem's discrete uniform distribution using the formula you have for a standard deviation for a discrete probability distribution. (Alternatively, you can simply use one of the two Excel's functions for calculating POPULATION standard deviations and apply that to the four integers, like this:
=stdevp(1,2,3,4)
)
If you do that, you will learn what the population standard deviation is for that distribution. Once you know that, then you just need to compute what 2.57 of those standard deviations would equal. Then you just need to find the next greatest integer, aka the ceiling, aka the minimum integer whose value is at least as big as 2.57 * SD, where SD is the standard deviation whose value you computed at the beginning of the problem.
If I'm interpreting that problem correctly, I suspect that the intent of the problem is to help the student get familiar with translating a word problem into a math problem and then apply concepts you learned early in the class about standard deviations and other parameters that describe key features of distributions.
Hope this helps gets you started on the other problems!
|
I should also note that the wording for that problem could be crucial. I've never seen a problem worded quite that way, so because of that, I'd caution you to make sure that you understand what the problem is asking for. The approach you described in your most recent post is off-track for the problem you described in the topic thread header, but it would not be too far afield for attacking another sort of problem in elementary probability courses, one that concerns what are called negative binomial distributions, so make sure you know what the problem really is!
