On line Study Group (1 Viewer)

[JMFH]

heyy guys im so retarded hey haha i cant figure out this one

Based on medical results, if apositive test is recorded what is the probabliity that you actually have the virus?
-------------------accurate -----not accurate----total
with virus:---------45----------------3-------------48
without virus-----922---------------30-----------952
Total:--------------967---------------33----------1000

would be much help asap coz im killing myself here haha thanks in advance!!!

jess

 

[ally147]

I also have a lot of difficulty with Sperical Geometry and also get confused with Probability... If anyone could throw some help my way it would be very very useful.

Any information would be helpful.

 

[elle_06]

Hey, does anyone happens to have any hints to help me understand direct and inverse variation, please?

To be more specific,

[1] What do they mean?
[2] What is the difference?

Thank you to anyone who can help =]

 

[PC]

Variation (or proportionality) is to do with the correlation between two different variables. There are two cases. When one variable increases, the second variable could increase or it could decrease.

Direct variation is the case where the first variable increases and the second also increases (proportionally).

Inverse variation is the case where the first variable increases and the second decreases (proportionally).

Strictly speaking, if A and B vary directly, then A is proportional to B.
If A and B vary inversely, then A is proportional to 1/B.

Now is the fun part. Dealing with variation is really simple. Where you see "is proportional to", replace it with "= k x".

So if A is proportional to B, then A = k x B, or A = kB.
If A is proportional to 1/B, then A = k x 1/B, or A = k/B.

After this, read the question. Somewhere you'll be able to find a value for A AND a value for B. Use these to find k, called the constant of proportionality.

Then use your modified equation to solve the problem.

Example: X varies inversely with the square of Y. When X = 400, Y = 20. Find the value of X when Y = 50.

So X is proportional to 1/Y².
So X = k x 1/Y².
Or X = k/Y².

Now when X = 400, Y = 20.
So 400 = k/20²
400 = k/400
k = 400 x 400
k = 160000

This means the equation is:
X = 160000/Y²
So when Y = 50, we have:
X = 160000/50²
= 160000/2500
= 64


Hope this helps!

 

[smely]

Hey everyone.. does anyone have thoe neep papers... u know the papers that are supposed to be REALLY hard??... our school has them but my maths teacher wouldnt give them to me because they use them when they write exams.... so does ANYONE have any?

 

[emanuellasker]

Hello happeninchick, I think your notes are really great. I just had one question, when do you know to use either one or two applications with simpsons rule? I looked through heaps of books but can't seem to find the answer. Any help would be really aprreciated.

 

[PC]

If you see three dotted lines in the diagram, then you'll do it twice. If there's only one dotted line then you'll do it once.

And most of the time the question will say anyway.

Failing that, just go with your gut feeling!

 

[emanuellasker]

Gee thanks PC. Much appreciated.

 

[emanuellasker]

Just wondering as well, would anyone be able to post up examples of the arc length formula as i still do not quite get it. Thnx

 

[emanuellasker]

Okay, would I be right in saying that the first numbers in a set of coordinates for a small circle are the same and vice versa for a large circle? e.g. 23*S, 127*E and 23*S, 145*E

 

[PC]

Provided they write the latitude co-ordinates first, then you'd be right!

The general convention all over the world is to write latitude first (that's North or South) and then longitude (East or West), but who knows what tricks they might throw in!

Also ... arc length formula.

Arc length = @/360 x 2πr

where r is the radius of the circle and @ is the angle of the sector.

So using your example, if A is (23°S,127°E) and B is (23°S,145°E) then A and B lie along the 23°S line of latitude, a small circle. The angle of the sector is 145 – 127 = 18°.

Now, because it's a small circle, you'd need to be told the radius of that small circle. You won't have to work it out for yourself. It's 5891 km.

So distance = @/360 x 2πr
= 18/360 x 2π x 5891
= 1850 km

Hope this helps.

 

[emanuellasker]

Yes it does, it helps quite a great deal thanks alot. I was just browsing through the hsc online website I got 100% for the questions relating to spherical geometry however the 1st question here http://hsc.csu.edu.au/maths/general/hsc/measurement/m6/m6_mc/M6_questions.html leaves me wishing to throw my calculator out the window. I have absolutely no idea how to do this, I think its the a over sina and b over sinb formula but i keep getting the wrong answer. Any help would be greatly appreciated. Thanks again PC for ur help thus far.

 

[omigodwhenover]

wrong answer oops...right answer later on

 

[emanuellasker]

Thank you so much omigodwhenover, you don't know how much you saved my life, not to mention my casio fx 82tl's life.

 

[emanuellasker]

Can anyone help me out with the last question on this page as well, http://hsc.csu.edu.au/maths/general/hsc/measurement/m6/m6_mc/M6_questions.html i'd be very much obliged. thnx

 

[omigodwhenover]

Can anyone help me out with the last question on this page as well, http://hsc.csu.edu.au/maths/general/hsc/measurement/m6/m6_mc/M6_questions.html i'd be very much obliged. thnx

omg im definitely helping u cuz we have the same calculator!! anyone with an fx82TL is a friend of mine lol!

This last question just requires 3 simple applications of cosine rule, and just to point out the obvious, angle XOY will be 360-120-130

 

[Dr_Doom]

You have to do 3 applications of the cosine rule...

I ended up with 399.03 which is not one of the answers :S...

 

[Dr_Doom]

omg im definitely helping u cuz we have the same calculator!! anyone with an fx82TL is a friend of mine lol!

This last question just requires 3 simple applications of cosine rule, and just to point out the obvious, angle XOY will be 360-120/130

don't you mean 360 - 120 - 130 = 110

 

[omigodwhenover]

don't you mean 360 - 120 - 130 = 110

yes i did! it was a typo sorry!

 

[omigodwhenover]

hey sorry but i realised i gave u the wrong method for the first question;
1. use simple trig ratios to find AC (sin 50* = 120/AC); AC = 156.6488747
2. use sine rule in triangle ACD to figure out x;
156.64.../sin 30* = x/sin20*
Therefore x = 107.1541412 or 107.2 correct to one decimal place

sorry for giving u the wrong answer before