Well, it's statistics and probabilities, but I couldn't figure out a better sub to post it. It's not exactly homework, it's an old exam exercise. I don't have a lot of time to learn the subject so I'm trying to figure out how to solve exercises from older tests.
The exercise gives you two populations of steel rods, population A containing 4 rods and population B containing 5 rods. The quantity measured for each bar is the weight they can take until they bend, measured in tons. For A, the mean is 18.6 and the standard deviation is 1.8, for B the mean is 17.8 and the standard deviation 2.1.
The first question requires you to find a 95% confidence interval for the ratio of the variances of populations A and B.
The second question asks you to check the hypothesis that the mean for bars of type A is higher than that of type B for 99% confidence (I am less than 99% sure I am confident in my understanding of what this means).
The third question gives you that A follows a distribution with a mean of 17.5 and a standard deviation of 2. It also gives you that a population of bars is considered acceptable if the mean is above 17, and asks you what the probability of a population of bars of type A to be "acceptable" is.
- I don't even know...
Now I don't really know much about the subject, I'm primarily just peaking into my textbook to see how to solve this or that exercise. I believe I can figure out how to solve the third question. However I couldn't find how to solve the first two. I know how to find a 95% confidence interval for, say, the mean or the variance or whatever of a population. But how do I determine the confidence interval for the ratio between the variances for two different populations with different sizes? I'm also a bit confused about what the second question wants you to do conceptually. Any help would be appreciated, and will probably help me pass my exams a lot.