Returning first exam. Starting Excel (I asked them to read the first section of the chapter – a tutorial – and bring their work to class. Let’s see how many did.)
Best class of the semester so far (I think). One student says she’s “fallen in love with Excel”. One said he was lost ten minutes ago. After suggesting that he should have asked when he first lost the thread I asked her to catch him up. Which she did.
Everyone did the first part of the Excel tutorial (Section 6.1) so I was able to start right away with what-if? – doubling the CEO salary increases the average from $77K to $87K even though only one salary has changed. All agreed that just reporting the change in the company annual report would be misleading. I promised to return to that at the end of the class. The point here was to show the power of what-if.
I also took the time to suggest saving early and often.
Then I gave back the exams (after making them promise to put them away when I asked them to) and drew this picture on the board. (What’s pasted here is Excel’s rendering of what I drew – see the discussion that follows.)
I reassured them about the curve – most of the low grades still led to C so far for the semester. Then I put up this table and we made Excel draw the histogram (I haven’t called it a histogram yet). I took the occasion to ask a meta question – how do you find out how to do something new in Excel (or anywhere). Possibilities: ask someone, search the web, just try, read the help. No one was interested in the last of these. I use the third. You should start with what suits your personality, but be prepared to switch if you have no success.
| 26-35 | 1 | ||
| 36-45 | 5 | ||
| 46-55 | 1 | ||
| 56-65 | 4 | ||
| 66-75 | 3 | ||
| 76-85 | 2 | ||
| 86-95 | 1 | ||
|
2 |
What is the average score?
Selecting the table and asking for the Excel =AVERAGE() function is a reasonable thing to try first. Turns out it just averages the numbers in the second column (ignoring the stuff in the first column). That’s 2.something. Common sense says that can’t be the average exam score.
The student who fell in love wrote out the list 30, 40, 40, 40, 40, 40, 50, … in Excel and found the AVERAGE. Brilliant, but tedious. The best part to rescue is using the middle of the range as the typical score for all the exams in that range. Excel can do the tedious part. I built a column with the midranges 30, 40, … with 30 and then =J13+10, cut and pasted down the column. That’s Excel guessing what you had in mind – sometimes useful, sometimes not. (Microsoft Word does that. Some students like it, some don’t). Then we multiplied to find 30*1, 40*5, … (again with cut and paste), summed those values, summed the number of exams and divided. Found an average something like 61, which makes sense.
I showed the power of what if by changing the 86-95 entry from 1 to 4, The average and the chart both changed.
With 10 minutes left I started in on the median – will redo that next time.
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