VCE Methods Question Thread!

[nt2387]

is 5B correct?

I am not too sure what you're doing with the working out.

"When there is a delivery" = given that.

So it would be Pr(X=2) + Pr(X=3) all divided by 0.7 (since the probability of a delivery is just 1- the probability of no deliveries)

[esthertham58]

Looks like you're trying to multiply the function v by ln(9). You need to write it as v(t)  or whatever your main variable is because in your current expression there's not actually any ts for your derivative to be a function so it interprets the expression to be a constant and is 0. That's why it's coming up as 'true' and not giving you a number.

Try this:

Code: [Select]

solve(d/dt(ln(9)*v(t)) = 0, d)



I'm not too sure what you mean. I've attached the question.  What did I do wrong?Thanks

[wyzard]

Looks like you're trying to multiply the function v by ln(9). You need to write it as v(t)  or whatever your main variable is because in your current expression there's not actually any ts for your derivative to be a function so it interprets the expression to be a constant and is 0. That's why it's coming up as 'true' and not giving you a number.

Try this:

Code: [Select]

solve(d/dt(ln(9)*v(t)) = 0, d)



I'm not too sure what you mean. I've attached the question.  What did I do wrong?Thanks

The reason it shows as true is because in the derivative, you plugged in a number into the function of v(t), which results in a number, and the derivative of it is 0.

Hence you're asking the CAS to solve for 0 = 0, which is obviously true. To fix that, replace by t, you'll obtain an answer in terms of t, then plug in the value .

[qwertyu1234567]

Hi guys, I can't seem to get my head around probability and need to fix this ASAP!
Could someone please help me with this question attached (it's from the 2015 VCAA exam 2)
Thanks so much

[esthertham58]

The reason it shows as true is because in the derivative, you plugged in a number into the function of v(t), which results in a number, and the derivative of it is 0.

Hence you're asking the CAS to solve for 0 = 0, which is obviously true. To fix that, replace by t, you'll obtain an answer in terms of t, then plug in the value .

Thanks for answering my question! So could you help me with the questions attached as I tried using the way you suggested but I'm not sure how to put it in the calculator. Thank you so much.

[qwertyu1234567]

Thanks for answering my question! So could you help me with the questions attached as I tried using the way you suggested but I'm not sure how to put it in the calculator. Thank you so much.

Hi, I've already done this question so I'll explain how I did it.

We are told that the minimum occurs when t=ln(9).
Given the equation for V(t), we know that we can find the minimum t value by differentiating V(t) and letting it equal 0
On the calc, we get t=ln(-2*(d-10)/d)
Now we can simply equate both of these equations and solve for d
Using the calc, d=20/11

[esthertham58]

Hi, I've already done this question so I'll explain how I did it.

We are told that the minimum occurs when t=ln(9).
Given the equation for V(t), we know that we can find the minimum t value by differentiating V(t) and letting it equal 0
On the calc, we get t=ln(-2*(d-10)/d)
Now we can simply equate both of these equations and solve for d
Using the calc, d=20/11

Oh I get it- Thanks

[qwertyu1234567]

Oh I get it- Thanks

No probs, can you help with my probability question above?^

[JellyBeanz]

No probs, can you help with my probability question above?^

Here is the solution to those questions. If you don't undersrand anything just lemme know.

Edit: Just be careful when rounding off. Take the full value of 0.6875 instead of rounding to 0.69 like i did to avoid intermediate errors.

[wyzard]

Hi guys, I can't seem to get my head around probability and need to fix this ASAP!
Could someone please help me with this question attached (it's from the 2015 VCAA exam 2)
Thanks so much

Say no more

a) is a typical continuous random probability distribution problem asking to find the probability of the random variable be within a range. To find the probability, simply find the area under the probability density function f(x) from 7 to 8, as it is zero from 8 onward:


b) This is a binomial distribution, as Mani chooses three at random, with each one has a certain chance of success. Hence n = 3, and p is the value obtained from (a)

c) Use the formula for the mean of a continuous random variable:


For problems involving continuous random variable, I'd highly recommend sketching the probability density function, as it will give you a much clearer idea on what's going on.

[esthertham58]

No probs, can you help with my probability question above?^

Sorry for the late reply-This is what I did. 

[esthertham58]

Sorry for the late reply-This is what I did. 

Just don't write " PUT in Cas" like I did

[qwertyu1234567]

Here is the solution to those questions. If you don't undersrand anything just lemme know.

Thanks so much! This helped a lot!

[qwertyu1234567]

Sorry for the late reply-This is what I did. 

Thank you!!!

[qwertyu1234567]

Say no more

Thank you! I think i get it now