An archive of Mark's Fall 2017 Intro Stat course.

# Homework problems?

blaiser1

I think I’ve encountered a few problems in this newest homework on what I believe is question 3. For part D it asks for the IQR which I know to be the difference between the first and third quartile. The correct graph above shows that the third is marked at 244 and the first is marked at 132, the difference between which is 112. However the program says the the difference is 32. Seeing as the standard deviation is 28 thats not possible. as well in part E, the section of the graph which contains the 15% with the highest cholesterol begins at 216mg/dl, but it says that that is also incorrect.

as well, problem two asks how many runs receivers 2 standard deviations under the mean get. Well the mean is 477 and the standard deviation is 376, so 2 standard deviations would leave you with negative runs which are not represented because I don’t think that is possible

mark

I think you’ve got a little typo and I guess you mean to say:

Regardless, those markings are not at the quartiles, rather they mark the number of standard deviations away from the mean. Thus, you can read the mean and standard deviation off of the graph. I guess the question is if you can use that to extrapolate the values of the quartiles from that other information.

shiller

Hi,

I had similar confusion with the runs scored by wide receivers because obviously from looking at the histogram we can see that the data is in no way a normal model. But I think the question wants us to assume that it is and use the 68-95-99.7 rule. In which case 95% of the data lies with 2 standard deviations below the mean and 2 above the mean. That means that 5% lie outside, with the 2.5% scoring more than 2 s.d.'s above and 2.5% scoring 2 standard deviations below. So I believe your answer is 2.5%. I hope that helps~ have a great weekend!