Things to look out for in the exams

[Stick]

Our teacher didn't teach it to us. Ask him when we go back.

[djsandals]

Hey could someone please clarify what the 'sliding line technique' is ? I dont remember this omg 

If you are doing a maximum/minimum problem for linear programming, and the co-ordinates of the vertices are not integers, but the problem requires them to be, you use the sliding line method to find out the maximum or minimum objective function values.

To do it, you must graph your objective function as a dotted line in red pen.  (Say if it's 2x+3y then just put a random value as your y-intercept, so you'd graph something like 2x+3y=6).

Then, grab your ruler and slide from the bottom to the top of your page if the gradient of the objective function is positive, and top to bottom if the gradient is negative.  (Whilst keeping the same slope as the objective function you've graphed)

The first point you hit is the minimum value, the last point you hit is the maximum value, and you can sub the last point that works into the objective function to get the maximum or minimum.

[lem]

Ok thank djsandals, yes I remember coming across one of these types of questions before thank you
+ 1 for you   

[djsandals]

Ok thank djsandals, yes I remember coming across one of these types of questions before thank you
+ 1 for you   

No worries

[astone788]

In CORE, After performing a transformation, you may need to make predictions using the new equation. Need to apply the same transformation to x before it is substituted into the equation.

[Yendall]

In CORE, After performing a transformation, you may need to make predictions using the new equation. Need to apply the same transformation to x before it is substituted into the equation.

This is very good advice. So many people would stuff this up. If for example it was an equation like: and you had to apply a reciprocal transformation of x to ensure linearity, you must linearise the x value when predicting from the original equation.

[StumbleBum]

Don't know how many schools use the Casio Classpad but an easy mistake to make with it is to use instead of as the standard deviation when reading it off the calculator.

Perhaps even make a calculator category if some other people have any other things to watch out for?

[Yendall]

Don't know how many schools use the Casio Classpad but an easy mistake to make with it is to use instead of as the standard deviation when reading it off the calculator.

Perhaps even make a calculator category if some other people have any other things to watch out for?

When I get home i might write up some CAS steps and errors to look out for. I think it'd be helpful, especially for stuff like Linearising Data and Residual Values/Plots.

[StumbleBum]

Don't know how many schools use the Casio Classpad but an easy mistake to make with it is to use instead of as the standard deviation when reading it off the calculator.

Perhaps even make a calculator category if some other people have any other things to watch out for?

When I get home i might write up some CAS steps and errors to look out for. I think it'd be helpful, especially for stuff like Linearising Data and Residual Values/Plots.

Oh yeh something else i've noticed (again only with the Classpad) is that when you input data values and prese (exe) it takes a fraction of a second to compute and if your putting values in quickly then sometimes you can miss a number.

[Yendall]

CAS Helpful Steps and Common Error Identifications

Frequency Recognition from a Histogram:
Move the cursor onto any column and a hand will show. Holding down the center button will display where the column starts and ends, also showing the frequency of the column displayed alongside the points.

Transforming Data Using Lists and Spreadsheets & Data and Statistics:
Add lists and spreadsheets and enter all appropriate formulas into seperate columns. I have saved mine as a document, this is what it looks like:


This will allow me to simply enter my data, and give me all transformation values, which allows for ease when plotting a scatterplot with regression:



From here I can plot any scatter-plot I wish:

[max payne]

Not sure if anyone else would ever make this mistake but, when your 'x' value is less than your 'x bar' value in the z-score formula, make sure you write the negative sign before you say someone is "x amount of standard deviations from the mean". Lost a mark. /cried

That's fairly routine, brenden, so I'm not going to put that on the list. However, it did remind me of another little trick which has popped up a little: when given an r^2 value and asked to find r, many people forget that the r value can be negative. A lot of people stuffed this up on my school's core SAC so I've put it up on the list.

Thats why you should always look at the graphs given to determine +/-r

[astone788]

[astone788]

Cop this:
An equation is made from a scatterplot of deseasonalised data. Use this equation to predict the sales in the first quatre of 2007. Because the questions wants us to predict the sales in the first quatre of 2007, it is implying the actual raw sales... NOT DESEASONALISE VALUES. This means you have to find the deasonalised figure by using the equation, and then convert this fiqure to its raw value by multiplying the deseasonalised figure by its corresponding seasonal index For example... (TSM 2007 1)

From a scatterplot of deseasonalised data of sales (in thousands of dollars) in 2006 a least
squares regression line is fitted. It is found to have the equation y = −1.4t + 22.8 . Some of the
seasonal indices for 2006 are given in the table.
Seasonal Index Q1 = 0.72 Q2 = 1.68
Assuming t = 1 is Quarter 1 of 2006, a prediction of the sales in the first quarter of 2007 using
this information is closest to
y = −1.4 X 5 + 22.8
   = 15.8 X Seasonal index (Q1)
   = 15.8 X .72
   = 11.367
   = C
A. $11.38
B. $15.80
C. $11376
D. $15800
E. $21944

Conversely, if the qustion had said predict the deseasonalised  sales in the first quatre of 2007, Then you wouldn't have to convert the deasonalised value to raw data.

Make sure you make this distinguishment. Back to studying 

[99.00]

IF IT SAYS 'CORRECT' TO TWO DECIMALS, THEN NEVER ROUND THE ANSWER UP
This was an error written in the 2007 exam 1:
Use this equation to find the mean surface temp for 2010 correct to two decimal places:
Mean surface temp = -12.361 + .013 X Year
Mean surface temp = -12.361 + .013 X 2010
Mean surface temp = 13.769
                               = 13.76 correct to two decimal places. 

NOTE: According to the  2007 VCAA assessment report the answer is 13.77 So they rounded the answer up. But the question says "correct to two decimal places." I asked my teacher and he said that VCAA made a mistake. So when the question says correct to 2 decimals - never round up!
Finally, my teacher said if the question says "to the nearest" THEN you must round answers up if possible.

What? Of course you can round up. The answer is 13.77

[Yendall]

IF IT SAYS 'CORRECT' TO TWO DECIMALS, THEN NEVER ROUND THE ANSWER UP
This was an error written in the 2007 exam 1:
Use this equation to find the mean surface temp for 2010 correct to two decimal places:
Mean surface temp = -12.361 + .013 X Year
Mean surface temp = -12.361 + .013 X 2010
Mean surface temp = 13.769
                               = 13.76 correct to two decimal places. 

NOTE: According to the  2007 VCAA assessment report the answer is 13.77 So they rounded the answer up. But the question says "correct to two decimal places." I asked my teacher and he said that VCAA made a mistake. So when the question says correct to 2 decimals - never round up!
Finally, my teacher said if the question says "to the nearest" THEN you must round answers up if possible.

Correct to two decimal places encompasses rounding. Correcting can be seen as another form of rounding. Always round if it asks for something correct to two decimal places, always