VCE Methods Question Thread!

[natdogg]

Not sure if this will help, but here's how I did it: (forgive me i dont speak latex)

I used rate (you called it speed) as the first formula. So I had Rj + Rm = 1/3.5

since you know that Rm = 1/5, you sub it in to find Rj, which is 3/35.

Tj = Oj/Rj = 35/3 which is the same as your answer

(is this even the right answer i have no idea)

[The Usual Student]

Not sure if this will help, but here's how I did it: (forgive me i dont speak latex)

I used rate (you called it speed) as the first formula. So I had Rj + Rm = 1/3.5

since you know that Rm = 1/5, you sub it in to find Rj, which is 3/35.

Tj = Oj/Rj = 35/3 which is the same as your answer

(is this even the right answer i have no idea)

Thanks! I was told my method was not correct but if you got the same answer then I don't see why it would be wrong!

[lzxnl]

Can someone point out what is wrong with my working out?
- Mary can clean an office in 5 hours
- Mary and john work together to clean an office in 3.5 hours
- how long does it take for john to clean a house?
I defined the variables as S=speed of cleaning one office per hours (output)
O= Output in terms of how many offices cleaned
T= Time
hence O=S x T or S=0/T
I said - Oj+Om=1
hence, since time taken was 3.5 hours
Oj= So x 3.5
Om=Sm x 3.5  Sm = 1/5 x 3.5 = 0.7

hence,
0.7 + 3.5 x So = 1
From there i worked out the So and then using So x T= 1 i figured out what T was......

I have a feeling i messed something up really obvious P.s My tutor said to do Tj+Tm=3.5 ... why is this better?

Your method is a little strange. What do you mean by 'output'?

I'm not sure why your tutor wants you to sum the times...you're not meant to in this question.

Let's break this down completely.
You're told that Mary works at some rate that cleans an office in 5 hours and that Mary + John clean the office in 3.5 hours. Clearly, if they're cleaning at the same time, their cleaning rates add. That's what you need to work out to sum.

Let this job be considered size 'S'
Let Mary's rate of finishing this job be M and that of John be J. S = rate * time
Then, 5M = 3.5 (M + J) = S
The time it takes John to clean the house is then S/J, which is what you want.
5M = 3.5 M + 3.5 J
1.5 M = 3.5 J -> J = 15M/35 = 3M/7 -> M = 7J/3
S = 5M = 35J/3
So S/J = 35/3

The problem with the working from others above is that they haven't explained where their working comes from.

[qazser]

Can someone point out what is wrong with my working out?
- Mary can clean an office in 5 hours
- Mary and john work together to clean an office in 3.5 hours
- how long does it take for john to clean a house?
I defined the variables as S=speed of cleaning one office per hours (output)
O= Output in terms of how many offices cleaned
T= Time
hence O=S x T or S=0/T
I said - Oj+Om=1
hence, since time taken was 3.5 hours
Oj= So x 3.5
Om=Sm x 3.5  Sm = 1/5 x 3.5 = 0.7

hence,
0.7 + 3.5 x So = 1
From there i worked out the So and then using So x T= 1 i figured out what T was......

I have a feeling i messed something up really obvious P.s My tutor said to do Tj+Tm=3.5 ... why is this better?

Izxnl has explained it well, but there's an easier way

Mary cleans 1/5 of the house in 1 hour
Together they clean 2/7 of the house in 1 hour

Therefore John clean 3/35 of a house an hour
Therefore it will take John 35/3 hours to clean the house.

[lzxnl]

Izxnl has explained it well, but there's an easier way

Mary cleans 1/5 of the house in 1 hour
Together they clean 2/7 of the house in 1 hour

Therefore John clean 3/35 of a house an hour
Therefore it will take John 35/3 hours to clean the house.

Indeed, that method works too, and is more elegant than mine.
I just wanted to provide a way of thinking about these problems that's applicable to other algebraic problems in general.

[qazser]

Indeed, that method works too, and is more elegant than mine.
I just wanted to provide a way of thinking about these problems that's applicable to other algebraic problems in general.

Yours would get the method marks, mine is lazy ahha

[The Usual Student]

Your method is a little strange. What do you mean by 'output'?

I'm not sure why your tutor wants you to sum the times...you're not meant to in this question.

Let's break this down completely.
You're told that Mary works at some rate that cleans an office in 5 hours and that Mary + John clean the office in 3.5 hours. Clearly, if they're cleaning at the same time, their cleaning rates add. That's what you need to work out to sum.

Let this job be considered size 'S'
Let Mary's rate of finishing this job be M and that of John be J. S = rate * time
Then, 5M = 3.5 (M + J) = S
The time it takes John to clean the house is then S/J, which is what you want.
5M = 3.5 M + 3.5 J
1.5 M = 3.5 J -> J = 15M/35 = 3M/7 -> M = 7J/3
S = 5M = 35J/3
So S/J = 35/3

The problem with the working from others above is that they haven't explained where their working comes from.

Yep, that clears a lot up! Thanks

[Adequace]

Can someone help me solve 2000=20pi*x^2 - (pi*x^3/3) for x? I tried but kept on getting stuck on different simplifications.

Thanks

[Peanut Butter]

Can someone help me solve 2000=20pi*x^2 - (pi*x^3/3) for x? I tried but kept on getting stuck on different simplifications.

Thanks

I haven't tried working it out yet, but is this an extended response question? It looks tech-active

[Adequace]

I haven't tried working it out yet, but is this an extended response question? It looks tech-active

Yeah, it's in the extended response part of the chapter review.

[Peanut Butter]

Yeah, it's in the extended response part of the chapter review.

Short answer = tech-free

Extended response = tech-active

Just plug it into your calculator and solve for x

[Springyboy]

Okay so Im getting a bit stuck on this question:
Find the equations of the lines that pass through the point (1,7) and touch the parabola y= -3x^2+5x+2
Hint: Form a quadratic equation and consider when the discriminant is zero

[qazser]

Okay so Im getting a bit stuck on this question:
Find the equations of the lines that pass through the point (1,7) and touch the parabola y= -3x^2+5x+2
Hint: Form a quadratic equation and consider when the discriminant is zero

lines, meaning linear equation that touches the line?

Assuming it touches (tangent line), we have to use calculus(idk if this q is intended to go into calc)

[qazser]

Say I solved a cubic equation for roots and found x = 3/2 to be a root. When I write the factorised form of the equation, would I write it with (x - 3/2) or (2x - 3)?

Both should be accepted as correct answers but (2x-3) looks nicer

[Springyboy]

lines, meaning linear equation that touches the line?

Yep that's what's it's looking for, how do I find the lines?