Homework 9
Math 114Q, Section 10

Due in class Tuesday, November 13.

  1. Redo the problems on the midterm exam. Since time is no problem on homework, try the extra credit problems too.

  2. In the last problem on the exam the most widely read newspaper seems to be USA Today. That may be because just about every hotel in the country puts a free one outside the door of each occupied room every night.

    Estimate the percentage of the weekly circulation of 2,293,137 for USA today is accounted for by all those automatically distributed copies.

  3. The data in the last problem on the exam gives circulation figures for the six months ending September 30. The table includes a column we didn't use: the percentage change in weekly circulation from its value in the previous six months (ending March 31).

    1. Use that data to construct a column in the spreadsheet giving each newspaper's weekly circulation for the six month period ending March 31. The best way to do this is to work out the first entry by hand. Using what we learned about percentages a month or so ago we can figure out that USA Today circulation for the period ending March 31 was 
            2293137
     ---------- = 2269534
     1 + 0.0104
      Now think about how to do that in Excel using the values in the first two cells in the table (2293137 and 1.04). Use that formula in the first cell of the next column, then copy it to all the rows.

    2. Create a double histogram showing both sets of circulation figures. Use intervals of size 100,000, and label the ranges with the number at the start of the range, so the table will look like this.

      You don't need to use columns B, C and D and start the numbers in row 34. I just did that here so I could talk about the table.) You can fill in the circulation range column by putting 300 in Cell B34, then the formula = 100+B34 in Cell B35, then copying that formula to all the cells in the column, as far as one that will contain 2200, the last interval you'll need.

      To draw the histogram, select the three columns of data B, C and D starting with row 33. Then Excel will label the series correctly for you.

      If you select starting with row 34 Excel will think the first column contains numbers, not labels, and will construct a weird column chart. Try that, just so you know what it will look like and can recognize that kind of error and fix it the next time you see it.

    3. Finally, we'll see that you can't average percentages.

      Compute the average circulation for the six month period ending March 31, by finding the total circulation and dividing by the number of newspapers (or just use the AVERAGE function in Excel).

      What is the percent change in the average from the period ending March 31 to the period ending September 30?

      What is the average of the percentages in the column labelled "percent change"?

      Do the two numbers you have computed agree? If not, which is the correct percent change in newspaper circulation from the first six month period to the second?