# A-Level S2 Maths Edexcel 25th June 2018 Unofficial Mark Scheme

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#1
Q1.
a) i) 0.8843
a) ii) 0.5662
b) 0.33
c) 0.0436418928

Q2.
a) 1: Fixed number of trials, 2: Probability of outcome is constant
b) 0.09375
c) 0.3437
d) 0.1694

Q3.
a) 2.5
b) 17/40
c) F(t) = {

0 for x&lt;1
1/4t^2 - 1/2t + 1/4 for 1&lt;x&lt;2
7/16t^2 - 1/16t^3 - 1/2t for 2&lt;x&lt;4
1 for x&gt;4
d) t = 1.894
e) 0.9375
f) 4/15

Q4.
a) alpha = -2, beta = 10
b) 107/240
c) 12/107

Q5.
a) As 0.1239 &lt; 0.05, there is insufficient evidence at the 5% significance level to reject the null hypothesis in favour of the claim
b) X&lt;/=10 and X&gt;/=25
c) 8 lies in the critical region, therefore there is sufficient evidence
d) 0.0367
e) n = 31

Q6.
a) show that (differentiate the c.d.f. to give the p.d.f., then differentiate the p.d.f., equate to zero and solve for a, by factoring k out)
b) 623/1280
9
3 years ago
#2
you parts 4b and 4c are wronf I believe, they are 107/240 and 12/107
20
3 years ago
#3
How does everyone remember their answer lol i can barely remember half of them
11
3 years ago
#4
I got n as 40?
6
3 years ago
#5
(Original post by ghfghgfg)
I got n as 40?
YES same here !!
3
3 years ago
#6
(Original post by GausIsTheBoss)
you parts 4b and 4c are wronf I believe, they are 107/240 and 12/107
I got the same
0
3 years ago
#7
(Original post by ghfghgfg)
I got n as 40?
n is 31

np was 200*0.2 which was fourty, which would've been the mean (and then you would approximate it to a normal distribution of mean 40 and standard deviation of root 32)
10
3 years ago
#8
I got the critical region correct, but for some reason said 8 is not in the critical region. How much marks is lost from that?
2
3 years ago
#9
(Original post by Mypenjustranout)
I got the critical region correct, but for some reason said 8 is not in the critical region. How much marks is lost from that?
1 mark
0
3 years ago
#10
for the approximation, you can only do
binomial=>normal
poisson=>normal
i did binomial approx and got 50 and most people got that
4
3 years ago
#11
(Original post by Sammy Arab)
Q1.
a) i) 0.8843
a) ii) 0.5662
b) 0.33
c) 0.0436418928

Q2.
a) 1: Fixed number of trials, 2: Probability of outcome is constant
b) 0.09375
c) 0.3437
d) 0.1694

Q3.
a) 2.5
b) 17/40
c) F(t) = {

0 for x<1
1/4t^2 - 1/2t + 1/4 for 1<x<2
7/16t^2 - 1/16t^3 - 1/2t for 2<x<4
1 for x>4
d) t = 1.894
e) 0.9375
f) 4/15

Q4.
a) alpha = -2, beta = 10
b) 29/48
c) 0.05

Q5.
a) As 0.1239 < 0.05, there is insufficient evidence at the 5% significance level to reject the null hypothesis in favour of the claim
b) X</=10 and X>/=25
c) 8 lies in the critical region, therefore there is sufficient evidence
d) 0.0367
e) n = 31

Q6.
a) show that (differentiate the c.d.f. to give the p.d.f., then differentiate the p.d.f., equate to zero and solve for a, by factoring k out)
b) 623/1280
Hey Sam, its Hass from KFA )
0
3 years ago
#12
(Original post by arjun0212)
for the approximation, you can only do
binomial=>normal
poisson=>normal
i did binomial approx and got 50 and most people got that
Why can't you approximate directly with normal? surely because np and npq > 5, its suitable to approximate with normal?
0
3 years ago
#13

My answers in no particular order
0
3 years ago
#14
(Original post by nisha.sri)
YES same here !!
Did you do the correction? As in -0.5
0
3 years ago
#15
(Original post by daisie)
Did you do the correction? As in -0.5
I got like 39.99 which basically rounds to 40. I did the approximation aswell as a continuity correction.

Edit: oh I just tried my calculation again and got 31.
2
3 years ago
#16
(Original post by wendychan)
Why can't you approximate directly with normal? surely because np and npq > 5, its suitable to approximate with normal?
thats what i did
np=40
sd=root32
0
3 years ago
#17
(Original post by Mypenjustranout)
I got like 39.99 which basically rounds to 40. I did the approximation aswell as a continuity correction.
I got 30.998 or something like that so I rounded to 31. I did the continuity correction as n-0.5-mean
3
#18
(Original post by GausIsTheBoss)
you parts 4b and 4c are wronf I believe, they are 107/240 and 12/107
In order to work out the probability that David was late, you add the probability that he overslept to the probability that he did not oversleep, multiplied by the probability that the train left in less than 5 minutes after 08:30.

Given alpha is -2, that suggests the train could possibly leave 2 minutes early, at 08:28, and this should be considered in the calculation.

(I'm assuming you calculated the probability that the train left between 0 and 5 minutes after 08:30)
2
3 years ago
#19
(Original post by arjun0212)
thats what i did
np=40
sd=root32
Yup thats what I did then you got your Z value as -1.68 and solved for (n-1/2) right ? I got then 30.99999 something so rounded to 31
0
3 years ago
#20
(Original post by daisie)
I got 30.998 or something like that so I rounded to 31. I did the continuity correction as n-0.5-mean
Yeah I just tried my calculation again and it got 31. Somewhere in my calculator I missed a number and got 40.

How much marks would be lost for this mistake. I did everything else correct, but just wrote the wrong number at the end.

I must have just thaught in my head 30.99 rounds to 40 :/
0
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