VCE Methods Question Thread!

[#1procrastinator]

The running times of movies at a theatre are normally distributed. If 21% of the movies run for longer than 118 minutes and 36% run for less than 92 minutes, find the mean and standard deviation.

[Jenny_2108]

The running times of movies at a theatre are normally distributed. If 21% of the movies run for longer than 118 minutes and 36% run for less than 92 minutes, find the mean and standard deviation.

Pr(X<92) = 0.36
Pr(X<118) = 0.79





Solve simultaneous equation, you get mean = 100, sd = 22.3

[VCEstudentguy]

How do I figure out the number of trials n on my Casio Classpad calculator if a binomial probability distribution with a Pr(success)=0.2 is required to have Pr(X<=1)=0.1?

[Jenny_2108]

How do I figure out the number of trials n on my Casio Classpad calculator if a binomial probability distribution with a Pr(success)=0.2 is required to have Pr(X<=1)=0.1?

Does your calculator have spreadsheet? I use Ti nspire though 

[VCEstudentguy]

Yeah, it does Ennjy. It's for 2010 Exam 2 Q2e by the way.

[#1procrastinator]

The running times of movies at a theatre are normally distributed. If 21% of the movies run for longer than 118 minutes and 36% run for less than 92 minutes, find the mean and standard deviation.

Pr(X<92) = 0.36
Pr(X<118) = 0.79





Solve simultaneous equation, you get mean = 100, sd = 22.3

Thanks...couldn't find that in my text

[Jenny_2108]

Yeah, it does Ennjy. It's for 2010 Exam 2 Q2e by the way.

lol I think other way is faster then spreadsheet
You type solve(0.8^x + nCr(x,1) * 0.2 * 0.8^x-1 = 0.1,x) then you get ans x=-3.8298 or x=17.947
So min trial =18

[pi]

You might need nsolve for that for some calcs ^^

[Jenny_2108]

You might need nsolve for that for some calcs ^^

I just try to type nSolve and it gives negative number. Wot!?!

[VCEstudentguy]

Yeah, it does Ennjy. It's for 2010 Exam 2 Q2e by the way.

lol I think other way is faster then spreadsheet
You type solve(0.8^x + nCr(x,1) * 0.2 * 0.8^x-1 = 0.1,x) then you get ans x=-3.8298 or x=17.947
So min trial =18

That was the first thing I tried, my answer was filled with factorials.

You might need nsolve for that for some calcs ^^

What is nsolve and where is it or is it just for TI-nspire?

[barydos]

Yeah, it does Ennjy. It's for 2010 Exam 2 Q2e by the way.

lol I think other way is faster then spreadsheet
You type solve(0.8^x + nCr(x,1) * 0.2 * 0.8^x-1 = 0.1,x) then you get ans x=-3.8298 or x=17.947
So min trial =18

That was the first thing I tried, my answer was filled with factorials.

You might need nsolve for that for some calcs ^^

What is nsolve and where is it or is it just for TI-nspire?

I remember getting lots of factorials with my Casio Classpad 330.
i dont think the calc likes solving for something with the nCr stuff in the equation

Pr(X=<1) = Pr(X=0) + Pr(X=1)
Pr(X=0) + Pr(X=1) = 0.1
nC0*0.2^0*0.8^n + nC1*0.2^1*0.8^(n-1) = 0.1
nC0 = 1 and nC1 = n
so that long equation is
0.8^n +0.2*0.8^(n-1) = 0.1
solve for n now, and you get your answer

[cnguyen599]

I'm having trouble with the 1st of question of the 2009 unit 4 exam (2).

The simultaneous linear equations
kx – 3y = 0
5x – (k + 2)y = 0
where k is a real constant, have a unique solution provided
A. k 􀂍 {-5, 3}
B. k 􀂍 R \{-5, 3}
C. k 􀂍 {-3, 5}
D. k 􀂍 R \{-3, 5}
E. k 􀂍 R \ {0}

The squares are supposed to be that E symbol. "Element of" I think that's what it's called.

[brightsky]

the two linear equations represent two lines on a cartesian plane. logically, the lines will intersect once if and only if their gradients are different. thus find the gradient of each line (this can be done quite easily by rearranging) and make them not equal each other. and then solve.

[Jenny_2108]

Or you can use matrix method. Do you remember det(A)=0 if there is no solutions or many solutions?
So in here, det(A)=-k(k+2)-5 * (-3)=0  when k=-5,3
Thus, unique solution for k E R\{-5,3}. Ans is B

[generalkorn12]

If Pr(A) = 0.3, and Pr(B)=0.6, and events A and B are independent, find Pr(A'|B).

I'm always intimidated by the words 'independent' or 'mutually exclusive', is there any way to make it less intimidating such as from the question above? The only way I make it less intimidating is by referring to the formulas....