Edexcel S2 - 27th June 2016 AM

How many marks was the P(7<R<10) question

Would I get any marks for this?! Question 5) Normal approx...X~B(n,0.2)E(X)=0.2nVar(X)=0.16ntherefore; X~N(0.2n,0.16n) P(X>55)=> CC P(X>=55.5)P(Z>(55.5-0.2n)/rt0.16n)=0.04011-P(Z<(55.5-0.2n)/rt0.16n)=0.0401P(Z<(55.5-0.2n)/rt0.16n)=0.9599Therefore;(55.5-0.2n)/rt0.16n = 1.7555-0.2n= 1.75(0.4)(n^1/2)55-0.2n=0.7n^1/2Then I squares out formed a quadratic and tried to rearrange but it didn't solve (yielded imaginary numbers) How many marks out of 8 would I get if any? Was I on the right lines or have I lost the plot.

Q1-
1.41=1.4419 so mean=varaiance so use poisson
0.2510
0.7769
0.1378
0.1516

Q2-
n=60
0.0133
0.0159
not sure about this one someone please reply to this one: 23.69%>1% accept H0.

Q3-
1/2
151PI/3 REPLY TO THIS as well PLZ

Q4-
B=8
A=-12
K=1/9

Q5-
N=225

Q6-
57


Q7-
1.2
0.24
41.875 AND 40 REPLY TO THIS ONE IT IS ABOUT THE MONEY LAST ONE.

Could you remind me of what the question was to the answer 0.7769

can't remember lol just typed in my calculator so i can keep it there till i get home to check answers

wow are you sure I thought it was 2 or 3 marks

THIS IS THE QUESTION FOR THE normal APPROX.

X-B(N,0.2) USING NORMAL APPROX AND GIVEN THAT P(X>55)=0.0401
FIND N

AND ANSWER:
X-B[N,0.2]= W-N[X,Y"] X IS MEAN Y" IS VARIANCE " MEANS SQUARED

P(X>55)=P[W>55.5)=P(Z>([55.5-X]/Y)=0.0401

P(Z<([55.5-X]/Y)=1-0.0401=0.9599

USING TABLE

(55.5-X)/Y=1.75
55.5-X=1.75Y
1.75Y+X=55.5 NOW USING THE BINOMIAL PARAMETERS
WE CAN FIND Y AND X IN TERMS OF N
X=0.2N
Y"=0.2*0.8N Y"=0.16N Y=0.4N! WHERE !=SQUARE ROOT
SO 1.75(0.4N!)+0.2N =55.5
0.7N!+0.2N=55.5
0.2N+0.7N!-55.5=0 NOW SOLVE THIS USING QUADRATIC FORMULA
YOU GET N!=15 OR (-18.5)
SO N = 225 OR 342.25 BUT WE ARE DEALING STUDENTS
SO N=225 ONLY
don't KNOW WHY PEOPLE ARE GETTING 200

Did anyone end up using logs for one of the questions - i can't remember the question but you had to find like the lowest value of Y or something and it involved the binomial ?

How many marks was the P(7<R<10) question

Did anyone else use simultaneous equations to find the value of k (and of course a being needed for that).

One of the simultaneous equations I used F(lower boundary)=0
and the other I believe I did F(upper boundary)=1 or something like that


Got k=1/9

I've done something very similar to you but I appear to have made a silly mistake, resulting in an answer of 124 or something from my quadratic formula. What do you think I might have lost in terms of marks?



Yes, I took ln of both sides and it appears I got the right answer, hope this is an OK method to use.. should be given that S2 is usually taught alongside A2 maths which includes ln in C3 and C4.

Anyone feel uncertain when they look at Q2 last part on hypothesis test ? the probability is like 0.2 given the significance level is 1%, that's a huge difference, in the past papers it was usually only little above or below significance level.