Stat 10 Midterm Result Notes

 

Mean =27

Standard Deviation =5 (4.91 to be exact)

Median =27

High =36 (2)

Low =12 (1)

 

There were 3 forms, there were no differences in the average scores between forms.

 

The total points were reduced from 40 to 36 because of one question, which was…

 

The Unemployment Data Question

            Basically everyone got 3 of the 4 problems correct.  We eliminated the last question in that set because no one got the 4th part right.  The distribution is not normal and while you can calculate a Z score, you should NOT because it's not going to be interpretable.  See the last notes on Lecture 7's handout.

            If you missed both parts b and c, please speak with your TA or with me.

 

The Frozen Pizza/Ice Cream/Seafood question

            Part A on every test involved finding the area for two different tails…so you had 2 Z scores that you needed to find and remember to subtract from 100 for each and then divide by 2 for each and then add the results together (phew).

            Part B was the "A" student question on the test.  If you got this one right, you are a good candidate for an "A" grade.  The trick here is to ask yourself "what is the nth percentile?" (it was either 30 and 70 or 25 and 75 depending on your test)  so if I have the 25th percentile, it's the value where 25% of the observations lie below this value and 75% above.  Once you figure that out, by symmetry, you could get the Z score for the other side.  You should have a picture like this:

 

 

 

Valid Z scores were .65 for the 25th/75th problem and .50 for the 30th/70th problem.

 

            Part C if the freezers are being improperly measured and they are ALL warmer than they should be, it's like adding degrees to the mean…this has the effect of shifting the distribution upward…you would need to recalculate Z scores to answer the question.  This would not change the temperatures required to store the food (the food just is, but freezers can be adjusted).  The trick here was to recognize this as a transformation (lecture 7)  So for example if the freezers originally have a mean of -5 but now they are 4 degrees warmer…