## Saturday, October 25, 2008

### Casio Classpad 330, Finding the mean and missing values

I posed the following question to my year 10's in order to continue our learning of the new calculator. It is an example of solving a problem where the mean is known but a value in the sample is not.

"Q: A class had 5 students. Student results in the last test was {50,56,64,72,81}. Isabella joined the class and the new mean became 68. Did Isabella score higher than the old mean and what was her score?"
H: If the mean of {50,56,64,72,81} is less than 68 then Isabella has scored higher as a higher score by Isabella will raise the mean. Since we know the new mean (68) we can work out Isabella's score by working backwards.
Set up a working pane with a main application and a list editor. Title a column 'list1'. Add the 5 student results to the list editor.

Click in the main application and type mean(list1) using the soft keyboard. Hit the blue exe button. The answer is 64.6 .
A: The old mean 64.6 is less than 68 therefore Isabella has scored higher.

To find Isabella's score click in the list editor and tap the next empty cell in list1. Press the x button. Click in the main application pane on the line that says mean(list1). Press the blue exe button.

This will return a sum to work out the mean of the list for values of and value of x i.e. (x+323)/6.

As we know the new mean alter the first line to read mean(list1)=68. Highlight the solution sum and tap Edit in the menu bar and then Copy. Paste the sum on the next line in the main application pane. Highlight the sum, tap Interactive on the menu bar, then tap Advanced on the sub menu and then tap solve. Tap ok at the base of the dialog box. The answer is x=85.
A: Isabella's test score was 85.