VCE General & Further Maths Question Thread!

[Fusuy]

Hey Guys; I have my first SAC next week Monday on Univariate and Bivariate Data (Half of the Core), just wondering if anyone has resources like practice SACs or Tests i could work through for preparation. Thank 

[Anchy]

What's the difference between a seasonal trend and a cyclic trend? :|

[MagicGecko]

What's the difference between a seasonal trend and a cyclic trend? :|

Well the essential difference is that a seasonal trend, as the name implies, display a specific pattern periodically (regular, predictable intervals). e.g ice-cream sales shoot up during summer.
But for Cyclic trends, the timing/patterns are a lot less predicable but you can see a pattern. e.g for the share price of Samsung phones, there will be a peak right when Samsung releases a new product but then it will slowly decrease.
So:
Seasonal --> pattern is regular and predicable (i.e showing the same pattern periodically)
Cyclic --> pattern is less predictable (i.e shows the same or similar pattern but not at the same moment every time, a peak may show up in march one year but august the next)

Hope that helped you somewhat

[2014year12]

Can someone help me out with this question I'm a little confused....
Thanks in advance!

[The Brightest Witch]

Can someone help me out with this question I'm a little confused....
Thanks in advance!

I keep getting $3, is that what's happening to you?

[2014year12]

I keep getting $3, is that what's happening to you?

I have no clue how to do it to be honest haha! How do you go about it?
The answer is D ($2.75) though if that helps? That is the closest to $3 I guess?

[The Brightest Witch]

I have no clue how to do it to be honest haha! How do you go about it?
The answer is D ($2.75) though if that helps? That is the closest to $3 I guess?

Ok so first I used the points (100,170) and (0,20) to get the gradient which was 1.5, and I'm pretty sure the y-intercept is 20, so my equation was C=1.5n+20.

So I subbed in 80 for n to get the cost of making of 80 apple pies, which was $140.

Then since they made a profit of $100, they would have to have sold those pies for $100 more than what it cost to make them, so they sold them for $240.

Then I divided $240 by 80 to get $3 per pie, and it looks nothing like any of the answers D:

[2014year12]

Ok so first I used the points (100,170) and (0,20) to get the gradient which was 1.5, and I'm pretty sure the y-intercept is 20, so my equation was C=1.5n+20.

So I subbed in 80 for n to get the cost of making of 80 apple pies, which was $140.

Then since they made a profit of $100, they would have to have sold those pies for $100 more than what it cost to make them, so they sold them for $240.

Then I divided $240 by 80 to get $3 per pie, and it looks nothing like any of the answers D:

I think that is correct, the book is just being stupid again don't worry haha!
Thanks for your help

[Einstein]

i know the 1/y reciprocal transformation is in the form 1/y=a+bx

i was doing doing part C and my equation was 1/y= 0.006+1x (1/y=0.006+x) and the answer has it as 1/y=x, i know the 0.006 is negligible but isn't the answer incorrect?

[MagicGecko]

i know the 1/y reciprocal transformation is in the form 1/y=a+bx

i was doing doing part C and my equation was 1/y= 0.006+1x (1/y=0.006+x) and the answer has it as 1/y=x, i know the 0.006 is negligible but isn't the answer incorrect?

0.006 is such a small number that it hardly makes a difference. If you were to still use 0.006 in your equation it won't make a different in your answer (unless you round to 3 decimal places). But in terms of VCAA exam, stick with your answer

[Einstein]

just a quick question in regards to residual plots. Say i did a x^2 transformation, i have x values in list one , y list 2, x^2 list 3 and residual values list 4 (casio class pad). When i do my residual plot, do i use my original x values or the new x^2 values and my residual values? i think you use original x? not sure, my residual plot always looks different to that of back of book when i try both variations

[The Brightest Witch]

just a quick question in regards to residual plots. Say i did a x^2 transformation, i have x values in list one , y list 2, x^2 list 3 and residual values list 4 (casio class pad). When i do my residual plot, do i use my original x values or the new x^2 values and my residual values? i think you use original x? not sure, my residual plot always looks different to that of back of book when i try both variations

Well you do your residual plot at first to 'show' that the data is curved and not linear, so you use the original x list.

But then I guess if you wanted to look at the residual plot for your transformed data, you could do one using x^2 or whatever which i do sometimes just to look at it for my own understanding, but yeah, the original is the one you're meant to use

[~V]

When they ask you to find residual values without given a table of x & y values and only the graph, is there a faster way to figure out residuals without having to create a table of values and go from there? It takes me a long time and reading off the graph can be really inaccurate as well...
Also, is log₁₀(y) and transformations the same thing?

[MagicGecko]

The only other way I can see you calculating the residuals without  reading from the graph is if the question also gives you a set of actual values. Which you would then use to create a regression line. From there its simply the case of
residual value = actual value - predicted value
Though I am quite sure you won't be asked to determine the residual from the graph alone, especially if its hard to make out the points (I haven't crossed any questions that do this...well at least none come to mind).

And no they are not the same.
A log₁₀(y) is called a log transformation whereas a 1/y is called a reciprocal transformation.
Basically they serve the same purpose, its just that the reciprocal transformation compresses the data to an even greater extent than the log transformation.

hope that cleared some things up somewhat

[Einstein]

do we need to know about how the log function works, ie. log10^etc.... the base etc.. , how we do in methods. Bit far-fetched for further though ahha