# 2017 HSC Mathematics Extension 2 paper thoughts? (1 Viewer)

#### shervos

##### Member
can someone explain the last question plz
i got 486
You probably got 486 by plugging values into the expression in the 2nd last part. However this gives the total number of ways under the assumption that not all colours have to be used.
To remove these cases, firstly note that it is impossible to use one colour to colour the grid, so we consider the cases with 2 colours. From 3 coliurs, we can choose 2 colours in 3c2 ways, and for each combination of 2 colours, there are two ways they can be used to colour the grid. So our final answer is 486-3c2*2 =480 as stated above

#### mkwon99

##### New Member
So let the three 3 colours be R, B and G,
R B R B
B R B R
and so on, while the R and B can switch spots => 2 ways
Since 3 colours must be painted at least once, we must find more cases like above
since this applies to any 2 colours, there are 3C2 ways to choose the colours
hence: total ways = 486 - 3C2 * 2

#### pikachu975

Rip arg(z/w) I did pi - tan^-1 (z/w) for some reason I turned retarded. Would I get 1/2

#### shervos

##### Member
Paper looked alright to me. Pretty uninspiring Q16 as per usual from the past few years
Yeah so it seems to be the case that while top students would've absolutely loved this exam cause free marks (or hated it because it was too easy and boring), students at the e3/borderline e4 level struggled with the paper.
This really reminds me of the case with the 2013 HSC paper

#### shervos

##### Member
I think I can safely say that NESA has run out of good questions to ask

#### Owlu

##### New Member
I thought they didn't give half marks

#### GiraCubed

##### New Member
I felt Questions 11-14 were great, and then 15-16 were the worse thing I've ever encountered. I choked some stuff in 15 but I basically felt I was doing an exam out of 85 after seeing 16.

I'm also sad that there wasn't more/tougher Mechanics questions in question 15/16. Really thought there'd be a Banked Track Q. Either way I'm trying not to think about the negatives lmao

#### pikachu975

Lol they ripped off integral of x tan^-1 x from trial papers

#### same1111

##### Member
screw q16 why the hell would do they do another probabilty question again when they did it last year. The first part of it was alright tho.. I didnt get the volumes question however.

##### -insert title here-
wow so easy this year

##### -insert title here-
I think I can safely say that NESA has run out of good questions to ask
but we haven't

they need to step up their game, or hire us to write questions.

#### Commando007

##### Member
You probably got 486 by plugging values into the expression in the 2nd last part. However this gives the total number of ways under the assumption that not all colours have to be used.
To remove these cases, firstly note that it is impossible to use one colour to colour the grid, so we consider the cases with 2 colours. From 3 coliurs, we can choose 2 colours in 3c2 ways, and for each combination of 2 colours, there are two ways they can be used to colour the grid. So our final answer is 486-3c2*2 =480 as stated above
So let the three 3 colours be R, B and G,
R B R B
B R B R
and so on, while the R and B can switch spots => 2 ways
Since 3 colours must be painted at least once, we must find more cases like above
since this applies to any 2 colours, there are 3C2 ways to choose the colours
hence: total ways = 486 - 3C2 * 2

thanks guys

#### pikachu975

RIP 9/10 in MC I didn't see the |z-1| for q3 I just did z so I typed in my calculator wrong

#### kibellion

##### New Member
when do u guys reckon answers will be up?

#### shervos

##### Member
when do u guys reckon answers will be up?
Not sure, but in the meantime you can point out specific questions and we'll write solutions for thise

#### shervos

##### Member
but we haven't

they need to step up their game, or hire us to write questions.
Yeah the bos trials are great actually.
Am disappointed that you let someone get over 70% though.

Naw I am just kidding, well done to both your team and that individual

#### pikachu975

Can someone please write a solution for 16b

#### calamebe

##### Active Member
Yeah the bos trials are great actually.
Am disappointed that you let someone get over 70% though.

Naw I am just kidding, well done to both your team and that individual
If you want, you can discount me as I did 4U last year, so then no one sitting the HSC this year got over 70%

#### shervos

##### Member
If you want, you can discount me as I did 4U last year, so then no one sitting the HSC this year got over 70%
Oh wow, I guess I'll retract my previous statement then.
Good on you either way - do you plan on pursuing mathematics in university?

#### marty3713

##### New Member
What mark do you guys reckon E4 cut-off will be around?