DESCRIPTION

Students:  Please keep in mind the OMSI rules.  Save your files often,
make sure OMSI fills your entire screen at all times, etc.  Remember
that clicking CopyQtoA will copy the entire question box to the answer
box.  

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*  IMPORTANT:  If your code works partially but on some parts either has *
*  syntax errors or results in an execution error, COMMENT OUT THOSE     *
*  PARTS SO THAT THE CODE DOES RUN.                                      *
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Don't forget to FREQUENTLY save and submit your work, even work    
in progress.  The network may get busy at the end of the exam     
period, making it difficult to submit then.  The server will shut
down at the appointed time, and NO further work will be accepted.
                                                                
In questions involving code which will PARTIALLY be given to you in the
question specs, you need to add new lines.  There may not be information
given as to where the lines should be inserted.  Do not modify the lines
already there unless instructed to do so.

If a question includes test code, make sure to include it in your
submission.

IF YOU FINISH EARLY, please leave the exam room.  If you stay, close
your laptop and sit quietly.

QUESTION -ext .R -run 'Rscript omsi_answer1.R'

This question will concern R's built-in 'airquality' dataset.  

First fit a linear model, predicting Ozone from all other variables
except Month and Day.  Print out the predicted Ozone for a day with
Solar.R = 188, Wind = 8.8 and Temp = 62.  (This is the same as the
conditional mean Ozone for those conditions.) Then print an approximate
95% confidence interval for that value.

Then fit another linear model, predicting Ozone from all other variables
except Day.  Print out the left and right endpoints of an approximate
95% confidence interval for the difference in mean Ozone for days in
May and days in July (i.e. the latter is subtracted from the former).

I recommend running table(airquality$Month) to get a sense of the data.

PROVIDE YOUR ENTIRE CODE, not just the print statements.

print('predict Ozone for a day with Solar.R = 188, Wind = 8.8 and Temp = 62:')
print(                         )
print('left and right endpoints of the CI:')
print(                         )
print('left and right endpoints of the CI:')
print(                         )