S2 Edexcel Tuesday 17th January SOLUTIONS IN FIRST POST

Original post by ilovemath

for proving k, if I showed I was using the quadratic but ONLY did the + solution not the minus would I get all the marks
so
k(k-1)=1
k² - k - 1

k = [1 + sqrt((-1)²-4(-1))]/2
k = [1 + sqrt(5)] /2

I would have thought you would need to state why you rejected the negative solution? I just said that k > 1 since 1 < x < k so -ve soln. rejected.

Reply 583

Original post by Luckyk

I did a two tailed test how many marks do you rekon ill lose for that??

Probably about 2, you get followthrough marks.

Reply 584

asas78978

Hey guys, I got F**ked up in this paper, I used Poisson for the number of sales in 10 calls and 20 calls, X-Po(1.5) and X-Po(3) can I get any mark for that? :frown:

and for the last part of last question I rejected H0 by mistake, but I wrote down the hypothesis and P(X>=13)=1-P(X<=12). And for number of calls I got 20 calls... X-Po(0.15a) where a=number of calls required.

Reply 585

ilovemath

2

Original post by Zhy

I would have thought you would need to state why you rejected the negative solution? I just said that k > 1 since 1 < x < k so -ve soln. rejected.

so will I get 3/4 marks?

Reply 586

Original post by ilovemath

so will I get 3/4 marks?

You will probably still get full marks for that question. I'd say at worst you'd lose just 1 mark...

Reply 587

oHellno

12

Even though it would be great to get 90+UMS why are people stressing so much about losing one or two marks? Because surely even if you just do 'okay' in this, you can still get an A* overall?

Reply 588

Original post by oHellno

Even though it would be great to get 90+UMS why are people stressing so much about losing one or two marks? Because surely even if you just do 'okay' in this, you can still get an A* overall?

I, like possible a few other people, want as close to 100 as I can possibly get so that I can afford to get below 90 when it comes to FP2/FP3.

Reply 589

Original post by oHellno

Even though it would be great to get 90+UMS why are people stressing so much about losing one or two marks? Because surely even if you just do 'okay' in this, you can still get an A* overall?

Very true for normal maths, but for A2 further maths you need 90% or over in 3 units to get an A*, and it's easier to get 90% in S2 than, say, FP3.

Reply 590

oHellno

12

Original post by Zhy

I, like possible a few other people, want as close to 100 as I can possibly get so that I can afford to get below 90 when it comes to FP2/FP3.

Original post by snow leopard

Very true for normal maths, but for A2 further maths you need 90% or over in 3 units to get an A*, and it's easier to get 90% in S2 than, say, FP3.

Ah okay that makes a lot more sense, cos I was thinking it shouldn't be a big deal for normal maths. Good luck for that!

Reply 591

Original post by asas78978

Hey guys, I got F**ked up in this paper, I used Poisson for the number of sales in 10 calls and 20 calls, X-Po(1.5) and X-Po(3) can I get any mark for that? :frown:

and for the last part of last question I rejected H0 by mistake, but I wrote down the hypothesis and P(X>=13)=1-P(X<=12). And for number of calls I got 20 calls... X-Po(0.15a) where a=number of calls required.

It seems many people (not just you) have done this. The mark scheme could be generous, but then again the statement before the actual question clearly mentioned probability rather than rate - this q may well have been testing whether a candidate could determine which distribution, Binomial or Poisson, was suitable.

Reply 592

ilovemath

2

ye many of my friends did this too!

Reply 593

Original post by snow leopard

It seems many people (not just you) have done this. The mark scheme could be generous, but then again the statement before the actual question clearly mentioned probability rather than rate - this q may well have been testing whether a candidate could determine which distribution, Binomial or Poisson, was suitable.

Why, though? n is not large (10). p is small (p < 0.2), but 10 isn't large. It seems unusual to put that...

Reply 594

Original post by Zhy

Why, though? n is not large (10). p is small (p < 0.2), but 10 isn't large. It seems unusual to put that...

Your question doesn't really make sense as those are the conditions are for an approximation; it assumes the binomial distribution. Before you even get to the binomial, there is the matter of choosing between Binomial/Poisson. Clearly it's Binomial as there is a 'proportion' of 0.15, but some people inferred a rate of 1.5 calls per hour or something.

(edited 12 years ago)

Reply 595

Xyonzz

I got everything right except that I did a two-tailed test. at the end of the day the question was undeniably poorly worded, but personally i think the fact that the probability found was less than 0.025 means that you could have done either, I've seen previous papers where they've done the same and in the mark scheme they provide for both one or two tailed. So i wouldn't stress about which tail, as long as you got the right probabilities etc it'll be 2 marks lost max :smile:

Reply 596

When are the official mark schemes, grade boundaries, etc. out?

Reply 597

Grade boundaries are out 7th March (the day before results day), and the mark scheme usually sometime before that.

Reply 598

Asukhwani

Hey Gibbo- think you got the last question on the exam wrong.

the P X is less than or equal to 12 if lambda=8 is 0.9362

NOT 0.9658.

Reply 599

like_a_star