!! HL Maths 2015 - predictions, guesses, Q & A, discussion ...

OMGeary · 07-06-2015 8:33pm

Kremin wrote: »

Why do you multiply by 4 factorial?

4 colours so you could pick any four first, then 3 second etc. So you multiply to account for this, I think.
Still don't get how it's 5 on top

MmmPancakes · 07-06-2015 8:37pm

skippy1977 wrote: »

Yeah take the mean age of students in your school. That would be the same as taking the mean age of every class...and finding the mean of those sample means.

ohhhhhhhh I get it, thanks!

pa limerick · 07-06-2015 8:39pm

What's definitions should I know for tomorrow and also what formula are not in the log tables?

skippy1977 · 07-06-2015 8:44pm

MmmPancakes wrote: »

ohhhhhhhh I get it, thanks!

Mmm you know what I may have oversimplified it a bit. You kind of had it actually the way you were explaining it.

The central limit applies for samples greater than 30 so lets say you take a large number of random samples of size 30 from the people in your school.

The mean of those sample means is the same as the mean age of student in your school.

The standard deviation of those sample means will not be the same as the standard deviation of ages in the school.
The standard deviation will be the standard deviation of the population divided by root n.

Sorry if I confused you a little!

MmmPancakes · 07-06-2015 8:58pm

Another question, when hypothesis testing, can you just use the z value? Do you only have to convert to p values if it says test using p values?

skippy1977 · 07-06-2015 9:02pm

MmmPancakes wrote: »

Another question, when hypothesis testing, can you just use the z value? Do you only have to convert to p values if it says test using p values?

It's a good idea to do both just incase. It further supports the case to reject or fail to reject.

I have a feeling that if they ask it they may lead you into the question as they did in the sample questions released.

They might first ask a confidence interval. Then a hypothesis test comparing z value (test statistic to critical values -1.96 and 1.96) and then the p-value. That would be a nice way of doing it!!

When the Hypothesis came up in 2010 for the Pilot schools the Marking scheme awarded full marks for a Hypothesis test for either doing the 95% CI, the z value OR the p-score. Any of the 3 methods got full marks.

I'd follow it up with a p-value. It will take a minute and you won't lose marks.

Dkey · 07-06-2015 9:06pm

Can someone give me sample questions to do with inferential statistics?

I didn't do the DEB mock so if someone could send me a photo of this question from mock and answers I would be thankful ^^

DarraghF197 · 07-06-2015 9:10pm

Nevermind this post if it doesn't relate to you!

Dkey · 07-06-2015 9:18pm

DarraghF197 wrote: »

Nevermind this post if it doesn't relate to you!

Ohh I wish we had this kind of probability question on paper, it is quite simple.

Just hope paper 2 will be easier than 1 ;x

Hon the Dubs · 07-06-2015 9:20pm

Anyone have solutions to Q4 on the DEB mock please?
I got the a and b but I can't get the c part at all... Please

numbers13 · 07-06-2015 9:26pm

Anyone have the marking scheme to the examcraft paper 2 mock? Looking for question 8 I think

Kremin · 07-06-2015 9:27pm

Hon the Dubs wrote: »

Anyone have solutions to Q4 on the DEB mock please?
I got the a and b but I can't get the c part at all... Please

Centre of circle (3,-1) radius = 2root10
Point (2,-8)
General Equation of tangents: y-y1=m(x-x1)
y+8=mx-2m
0=mx-y-2m-8
a:m b :-1 c: (-2m-8)
Distance from centre to (2,-8) = radius
Using perpendicular distance formula..
|ax1+by1+c|/root a^2+b^2....

|3m+(-1)(-1)+(-2m-8)|/rootM^2+1=2root10

|m-7|=2root10(rootm^2+1) (simplify the absolute value and cross multiply)
Square both sides (so the absolute value is always positive)
m^2-14m+49=40m^2+40
0=39m^2+14m-9
m=1/3 or m=-9/13

Hon the Dubs · 07-06-2015 9:29pm

Kremin wrote: »

Centre of circle (3,-1) radius = 2root10
Point (2,-8)
General Equation of tangents: y-y1=m(x-x1)
y+8=mx-2m
0=mx-y-2m-8
a:m b :-1 c: (-2m-8)
Distance from centre to (2,-8) = radius
Using perpendicular distance formula..
|ax1+by1+c|/root a^2+b^2....

|3m+(-1)(-1)+(-2m-8)|/rootM^2+1=2root10

|m-7|=2root10(rootm^2+1) (simplify the absolute value and cross multiply)
Square both sides (so the absolute value is always positive)
m^2-14m+49=40m^2+40
0=39m^2+14m-9
m=1/3 or m=-9/13

Thank you! I found my mistake, I changed a minus to a plus by accident lol
Thanks and best of luck tomorrow

Kremin · 07-06-2015 9:32pm

Does anyone know how to calculate a p value? it was a question on the debs mock and no sign of it in the tables book o_O

Hon the Dubs · 07-06-2015 9:34pm

Kremin wrote: »

Does anyone know how to calculate a p value? it was a question on the debs mock and no sign of it in the tables book o_O

I can help you here

It's 2[p(z>z-score from 95% interval)]
Lol probably didn't help I've written out a bit weird...

Kremin · 07-06-2015 9:40pm

Hon the Dubs wrote: »

I can help you here
It's 2[p(z>z-score from 95% interval)]
Lol probably didn't help I've written out a bit weird...

And the Z score is x-u/s/rootn right?

Is the P value for a sample with x=1150 u=1000 S.D=400 and n=60, 0.0038?

Also for the question on a test of cars where n=300, 78 were silver.
is the confidence interval .235<CI<.285? (Proportional interval)

Magnate · 07-06-2015 9:43pm

Ugh I don't get this new inferential stuff at all. I know it's easy and I was able to do it months ago when we covered it in class but it's just not clicking now and there's no time left

Dexster555 · 07-06-2015 10:10pm

Anyone know Wat trig proof likely come up

MmmPancakes · 07-06-2015 10:11pm

Kremin wrote: »

And the Z score is x-u/s/rootn right?

Is the P value for a sample with x=1150 u=1000 S.D=400 and n=60, 0.0038?

Also for the question on a test of cars where n=300, 78 were silver.
is the confidence interval .235<CI<.285? (Proportional interval)

Your answer is correct

z = x-u/(s/rootn) = 1150-1150/(400/root6) = 2.90
2.90 -> 0.4981
1 - (2 x 0.4981) = 0.0038 for those who dont get it

skippy1977 · 07-06-2015 10:15pm

Dexster555 wrote: »

Anyone know Wat trig proof likely come up

Unfortunately no pattern yet.

They have asked
cos 2A (the easiest one) in 2014
Sine Rule in 2013
...and that's it!

They can ask things twice in a row too. Theorem 11 in 2010 and 2011

Kremin · 07-06-2015 10:17pm

skippy1977 wrote: »

Unfortunately no pattern yet.

They have asked
cos 2A (the easiest one) in 2014
Sine Rule in 2013
...and that's it!

They can ask things twice in a row too. Theorem 11 in 2010 and 2011

Yeah, chances are a trig proof won't even appear honestly.

MmmPancakes · 07-06-2015 10:18pm

Kremin wrote: »

Yeah, chances are a trig proof won't even appear honestly.

Don't jinx it, it would be lovely if one or two came up

Kremin · 07-06-2015 10:18pm

Magnate wrote: »

Ugh I don't get this new inferential stuff at all. I know it's easy and I was able to do it months ago when we covered it in class but it's just not clicking now and there's no time left

We never even covered it in class :l. I remember him saying something about sampling but it was like in 2 mins just before we were let go from school so I really can't remember anything.

MmmPancakes wrote: »

Don't jinx it, it would be lovely if one or two came up

I'd love one too, I don't know why but I get a sense of pleasure when I write the proofs for things like that. It's one thing knowing, okay heres these identities i don't need to remember and Okay heres these identities I know where theyre from and how they got there.
It's kinda funny actually, can't remember the geometry proofs for ****, but I remembered the Applied Maths inertia proofs the first time I did one :l

DarraghF197 · 07-06-2015 10:22pm

The nice Tan proof like in the mocks would be welcome!

By the way, do we have to say QED for Trig proofs as well?

Blue giant · 07-06-2015 10:26pm

DarraghF197 wrote: »

The nice Tan proof like in the mocks would be welcome!

By the way, do we have to say QED for Trig proofs as well?

I write quod erat demonstrandum after everything

Kremin · 07-06-2015 10:30pm

DarraghF197 wrote: »

The nice Tan proof like in the mocks would be welcome!

By the way, do we have to say QED for Trig proofs as well?

I write QED after anything that requires any type of proving, dont know why lol..

Like even if it says Show x=2a or some crap, i write QED at the end.

DarraghF197 · 07-06-2015 10:30pm

Blue giant wrote: »

I write quod erat demonstrandum after everything

Hahaha full marks for you!

If there's like a really hard question that comes up and I get it out finally, I might write QED on it

Especially one of those geometry ones that can be a mess. It just feels so satisfying writing it down.

Kremin wrote: »

I write QED after anything that requires any type of proving, dont know why lol..

Like even if it says Show x=2a or some crap, i write QED at the end.

No harm in writing it down or so! Getting the right answer technically should have 'what was to be proved' beside it :P

12hello345 · 07-06-2015 10:51pm

can we be asked to derive the cosine formula??

skippy1977 · 07-06-2015 10:55pm

12hello345 wrote: »

can we be asked to derive the cosine formula??

Yep..one way is based on drawing a triangle in the unit circle something like this.

Then you use the distance formula to find the distance from (c cosA, c sinA) to (b,0) and you end up with the cosine rule!

12hello345 · 07-06-2015 11:17pm

skippy1977 wrote: »

Yep..one way is based on drawing a triangle in the unit circle something like this.

Then you use the distance formula to find the distance from (c cosA, c sinA) to (b,0) and you end up with the cosine rule!

why is it '(c cos A, c sin A)' like whats the 'c' about??

!! HL Maths 2015 - predictions, guesses, Q & A, discussion ...

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