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

Yh same here i meant the root of variance. I dont even know what went wrong some people also got 40

you parts 4b and 4c are wronf I believe, they are 107/240 and 12/107

For question 4. E(X) =4. What was Var(X) equal to?

GUYS MY MISTAKE. It was 31!! I literally read 30.99 from my calculator as 39.99 . WOOPS 😂

E(X) was actually 5/2

Everyone got the same answer as me . Idk what your method is but I'd love to see it.

I recognise those numbers, so I think I got those.

Exactly the same thing I did XD

I got b as -1/20 and I as 1/15 or something of that sort

same and the probability was like 3/4 or1/4 can't remember

You sure E(X) was 5/2 and not 4?

I got b as -1/20 and I as 1/15 or something of that sort

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

For question 4. E(X) =4. What was Var(X) equal to?

I can’t actually remember what I wrote about the probability of the person being late but what I did was Add the probability of him oversleeping to the probability of t being bigger that or equal to 5??!

I did that aswell. Idk if it’s correct tho :/.