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#1 Re: Help Me ! » Permutation question » 2010-09-05 03:35:24

Carisma
bobbym wrote:

Hi all;

Hi Bobby,

Thanks for this! I always tend to over complicate things with these permutation questions.

#2 Help Me ! » Permutation question » 2010-09-05 01:25:35

Carisma
Replies: 6

A committee of five people is to be chosen from 5 married couples. In how many ways can the committee be chosen if:

a. the committee mus contain at least one man and one woman
b. the committee must contain the youngest man
c. both husband and wife cannot be on the committee


I've managed to do the 1st 2 parts but for some reason I keep getting the last part wrong...the answer's 32 and I'm getting something different.

#3 Re: Help Me ! » Points of Inflection.. » 2010-08-31 03:26:19

Carisma
bob bundy wrote:

Hi Carisma,

At a maximum the gradient changes from + to - as you pass through the point, and from - to + for a minimum.

At a point of inflexion the gradient doesn't change sign as you traverse the point.

So once you have the differentiated function, checking the gradient just left of the potential point and just right will give you definitive evidence. 

Bob

Thanks Bob! This cleared up my confusion with the differences in concavity around maximum/minimum points and points of inflection

#4 Re: Help Me ! » Points of Inflection.. » 2010-08-31 03:25:03

Carisma
bobbym wrote:

Hi;

Yes, those are the possible points of inflection. There is more to do.

The x's are correct I don't know where you are getting those y values from. But it is not important.

Check those x's for concavity changes in f''(x).

I found the y value by substituting the x values into f(x)...am I doing this wrong?

I have checked the concavity on both sides of the x values and it is positive on both sides when x = 0.5 and when x=-0.5

#5 Re: Help Me ! » Points of Inflection.. » 2010-08-31 00:26:07

Carisma

Hi,

I found the second differential, solved for 0 then found the y- coordinate and I got the 2 points of inflection to be (0.5,0.606) and (-0.5, 0.606)

Is this correct?

And thank you for helping smile

#6 Help Me ! » Points of Inflection.. » 2010-08-30 22:52:42

Carisma
Replies: 8

I'm just a bit confused with this question, I've found the second derivative, but it looks more like a maximum to me than a point of inflection:

Consider the curve with equation f(x) = e^(-2x^2) for x<0. Find the co-ordinates of the point of inflection and justify that it is a point of inflection.

Thank you for any help in advance!

#7 Help Me ! » Implicit Differentiation... » 2010-08-03 01:02:20

Carisma
Replies: 2

I have to implicitly differentiate the following and then form an equation for dy/dx:

xy/π + sinxlnx = cosx + 1

I then have to show that the gradient is lnx when x=π.

I have tried doing it several times but it seems i keep getting the wrong answer.

Any ideas?

Thanks so much in advance!

#8 Help Me ! » Question about Cumulative distribution/Probability density functions » 2010-05-16 07:21:21

Carisma
Replies: 1

The random variable X metres represents the ase of a rectangle of area 1metre^2. The height is represented by the random variable Y metres. X has uniform probability density 1 over the interval 0<X<1.

Deduce the cumulative distribution function for the height, G(y) = P(Y<y).

Thank you for helping in advance smile

#9 Help Me ! » Probability and Combinations/Bayes Theorem » 2010-04-08 03:47:32

Carisma
Replies: 1

In a class, there are 30 students. 12 students hope to go to university A, 8 students hope to go to university B, 4 students hope to go to university C and 6 students hope to go to university D.

A) 4 students are picked at random.
i) What is the probability that all 4 hope to go to university A?
ii) What is the probability that all 4 hope to go to the same university?
iii) Given that the first person picked hopes to go to university A, what is the probability that the other three hope to go to university B?

B) Find the probability that exactly 4 other students will be selected before a student who hopes to go to university C is selected.


Thank you for any help smile

#10 Help Me ! » A probability sets question...please help:) » 2010-01-08 01:19:00

Carisma
Replies: 4

Given that events A and B are independent with P(A n B)=0.3 and P(A u B')=0.3, find P(A u B).

It's supposed be quite basic as its only 3 marks, but I think I'm missing something as I can't figure it out...anyone know?

Thank you for your help smile

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