IB Maths Marathon (1 Viewer)

davidgoes4wce

Well-Known Member
Joined
Jun 29, 2014
Messages
1,878
Location
Sydney, New South Wales
Gender
Male
HSC
N/A
Re: International Baccalaureate Marathon

Was going through worked example from Cambridge tonight and there was a mistake in the working out for part (c), vector BC should be -2-k. Small mistake but its important that I point it out to all IBers in 2017:

 

boredofstudiesuser1

Active Member
Joined
Aug 1, 2016
Messages
570
Gender
Undisclosed
HSC
2018
Re: International Baccalaureate Marathon

Was going through worked example from Cambridge tonight and there was a mistake in the working out for part (c), vector BC should be -2-k. Small mistake but its important that I point it out to all IBers in 2017:

Wow, how much maths do you do a day?
 

InteGrand

Well-Known Member
Joined
Dec 11, 2014
Messages
6,109
Gender
Male
HSC
N/A
Re: International Baccalaureate Marathon

Was going through worked example from Cambridge tonight and there was a mistake in the working out for part (c), vector BC should be -2-k. Small mistake but its important that I point it out to all IBers in 2017:

What do you mean? The vectors b and c have no k, so vector BC would have no k.
 

InteGrand

Well-Known Member
Joined
Dec 11, 2014
Messages
6,109
Gender
Male
HSC
N/A
Re: International Baccalaureate Marathon

The area values you got are all very close. Haven't checked your calculations but if they're all right, the small discrepancies would just be due to the fact that you used rounded values for the angle.

 
Last edited:

davidgoes4wce

Well-Known Member
Joined
Jun 29, 2014
Messages
1,878
Location
Sydney, New South Wales
Gender
Male
HSC
N/A
Re: International Baccalaureate Marathon

Not sure what the best way to study for sequences and series, whether it be HSC or IB but should we tell the students to memorise the formulae (even though the formuale sheet is provided)?
 

davidgoes4wce

Well-Known Member
Joined
Jun 29, 2014
Messages
1,878
Location
Sydney, New South Wales
Gender
Male
HSC
N/A
Re: International Baccalaureate Marathon

OK problem solved if you guys are familiar with the Casio fx-9860G AU, you should leave the fraction to the right and not cross multiply in Solver.





 

davidgoes4wce

Well-Known Member
Joined
Jun 29, 2014
Messages
1,878
Location
Sydney, New South Wales
Gender
Male
HSC
N/A
Re: International Baccalaureate Marathon

This is a Band 7 IB question (equivalent to a HSC Band 6 aiming for 95%+ on paper)



With regards to (b) , would it be OK to not write the answer involving sequences? i.e doing it manually in order to get the marks







My way I did it was just using the 'common sense method':



Notice both answers do give slightly different decimal values .
 
Last edited:

seanieg89

Well-Known Member
Joined
Aug 8, 2006
Messages
2,662
Gender
Male
HSC
2007
Re: International Baccalaureate Marathon

This is a Band 7 IB question (equivalent to a HSC Band 6 aiming for 95%+ on paper)



With regards to (b) , would it be OK to not write the answer involving sequences? i.e doing it manually in order to get the marks







My way I did it was just using the 'common sense method':



Notice both answers do give slightly different decimal values .
0.892 and 0.655536 are wrong. By doing it manually like this you are greatly increasing the number of points at which you can mess up the calculation. And of course this won't be feasible if 9 is replaced by 1000.

The correct answer is the expression t8 (although the 2 is +2, not -2), which in decimal form is exactly 15.31564544.

Ps. alarm bells should be ringing in your head at "slightly different decimal values". The only step in which any rounding is involved is at the very end, so these answers should coincide exactly prior to rounding, which they clearly don't.
 
Last edited:

davidgoes4wce

Well-Known Member
Joined
Jun 29, 2014
Messages
1,878
Location
Sydney, New South Wales
Gender
Male
HSC
N/A
Re: International Baccalaureate Marathon

0.892 and 0.655536 are wrong. By doing it manually like this you are greatly increasing the number of points at which you can mess up the calculation. And of course this won't be feasible if 9 is replaced by 1000.

The correct answer is the expression t8 (although the 2 is +2, not -2), which in decimal form is exactly 15.31564544.

Ps. alarm bells should be ringing in your head at "slightly different decimal values". The only step in which any rounding is involved is at the very end, so these answers should coincide exactly prior to rounding, which they clearly don't.
I'm aware that there was a slight error with my working out but in terms of 'method' of getting to the answer, there are 2 methods in order to get to the right answer.

Would my method be suitable in order to answer a question like this, whether it be HSC and/or IB?
 

seanieg89

Well-Known Member
Joined
Aug 8, 2006
Messages
2,662
Gender
Male
HSC
2007
Re: International Baccalaureate Marathon

I'm aware that there was a slight error with my working out but in terms of 'method' of getting to the answer, there are 2 methods in order to get to the right answer.

Would my method be suitable in order to answer a question like this, whether it be HSC and/or IB?
Depends what you mean by suitable.

a) Will the answer be the same?
Yes, obviously. Summing a geometric series manually will give you the same result as applying the formula for the sum of a geometric series.

b) Will markers treat the solution as being equally valid?
I don't know the marking criteria, but I can't imagine any reason why not.

c) Do I recommend manually summing geometric/arithmetic series?
Definitely not, unless the series is only a couple of terms long. As I said in my previous post, you are greatly increasing the number of places at which you can make mistakes. The method is also slower (assuming proficiency with both), and not feasible for series with many terms. You need to know how to sum general arithmetic and geometric series for the course anyway, so why not use this knowledge?
 

davidgoes4wce

Well-Known Member
Joined
Jun 29, 2014
Messages
1,878
Location
Sydney, New South Wales
Gender
Male
HSC
N/A
Re: International Baccalaureate Marathon

Yep thanks for your response.

I did some vector cross product before , a large chapter was devoted to that in Calculus Stewart book. I remember when I did 2nd year Engineering, I spent a lot of time doing those questions. It's a very efficient way of calculating an area.
 

davidgoes4wce

Well-Known Member
Joined
Jun 29, 2014
Messages
1,878
Location
Sydney, New South Wales
Gender
Male
HSC
N/A
Re: International Baccalaureate Marathon















The answer in the book states that ' ..for the first 19 years

Want to check if I could say something along the lines of '18 years and 11 months or if we could leave the answer as a decimal (with 1 d.p), 18.4 years?

 

He-Mann

Vexed?
Joined
Sep 18, 2016
Messages
279
Location
Antartica
Gender
Male
HSC
N/A
Re: International Baccalaureate Maths Marathon

If you were pedantic, then expressing your answer in years only is more appropriate since our question was with respect to years. i.e. maintain consistency of units
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top