AQA A2 Mathematics (Old Spec) - Statistics 2 MS2B - 19 June 2018 [Exam Discussion]

Never seen the last question before using a continuous distribution but I used the formula book to get integral of (1/x)(f(x))dx and for E(X^2) integral of (1/x^2)(f(x)) dx. I think I got 11/900 but honestly can't remember. Also found a couple of the worded answer questions hard.

What do you think for grade boundaries? I'd say like 3 marks lower than last year as it definitely seemed harder to me.

I also got c =20, 90th percentile = 19, median = 15.0

(edited 5 years ago)

i got 20 for c

Original post by Dorsia1

Never seen the last question before using a continuous distribution but I used the formula book to get integral of (1/x)(f(x))dx and for E(X^2) integral of (1/x^2)(f(x)) dx. I think I got 11/900 but honestly can't remember. Also found a couple of the worded answer questions hard.

What do you think for grade boundaries? I'd say like 3 marks lower than last year as it definitely seemed harder to me.

I also got c =20, 90th percentile = 19, median = 15.0

I did the same for the last question. Just substituted X for (1/X) in the formulas for E(X) and E(X²) to get Var(X). I got 11/900 in like the last second haha! Now I'm thinking, I can't even remember what I got for the 90th percentile. '19' sounds familiar, but I didn't save it on my calculator~

For me it was slightly harder than last year. I'd be guessing maybe 65/57/50 for A*/A/B...
Last year was 67/59/51...

Reply 23

BalrajSingh

2

for Q1) I found the area of the triangle was 0.4

so rectangle
0.6=0.1(c-16)

got c=22

Median as 17
and
90th as 19

Reply 24

Dfhdidjhssjj

2

I found there is a log number in the last question part b Did anyone else got the same?

Reply 25

Anonymouspsych

16

i thought it was pretty good, probably lost a few marks on the wordy stuff like commenting on blah

Reply 26

Harj2807

7

I got 20, 19 and 15 for question 1 too. Got 11/900 for the last question too. 5p as the expected value of the game(discrete one). Type 2 error for the second hypothesis test and 14.2 for chi squared from what I can remember.

Reply 27

Hally Bee

1

What did everyone do for question 2 where it was asking about the mean prize money and standard deviation???

Reply 28

ARandom1002

3

dammit for last question i found out var(x) normally missed the 1/x how many marks do you think i lose :frown:

?

Reply 29

Anonymouspsych

16

Original post by Harj2807

I got 20, 19 and 15 for question 1 too. Got 11/900 for the last question too. 5p as the expected value of the game(discrete one). Type 2 error for the second hypothesis test and 14.2 for chi squared from what I can remember.

i put -5p what was the exact question lol

Reply 30

jess2157

8

Original post by Harj2807

I got 20, 19 and 15 for question 1 too. Got 11/900 for the last question too. 5p as the expected value of the game(discrete one). Type 2 error for the second hypothesis test and 14.2 for chi squared from what I can remember.

I couldn't even do that question about the prizes and that game. I guess you had to find E(X) and then find the value of the mean prize/amount paid (can't remember what it was)? I couldn't figure out to do E(X) because it said '7 or less' on one of the probabilities...

I got the same Chi-squared and hypothesis answers though.

Reply 31

kilburn21

3

Does anyone remember what the limits were for the last question?

Reply 32

Harj2807

7

Original post by Anonymouspsych

i put -5p what was the exact question lol

It was work out the expected value of the prize and show that the standard deviation lies better 33p and 34p

Reply 33

Anonymouspsych

16

Original post by Harj2807

It was work out the expected value of the prize and show that the standard deviation lies better 33p and 34p

well i thought since the prize is what the player wins the -5p tells you that on average the person will lose money. I got a standard deviation of about 33.4

Reply 34

Harj2807

7

Original post by jess2157

I couldn't even do that question about the prizes and that game. I guess you had to find E(X) and then find the value of the mean prize/amount paid (can't remember what it was)? I couldn't figure out to do E(X) because it said '7 or less' on one of the probabilities...

I got the same Chi-squared and hypothesis answers though.

I was struggling on it for ages and I did soemtjing and the standard deviation worked in the last 5 mins. I did the probability of x=8,9,10 times there prize values for E(x) then squared the money for E(x^2) and then took them away and it somehow worked. I just ignored the 7 or fewer one since it had no money attached to it.

Reply 35

Lala~

17

How many marks were all the crv and drv questions worth? A rough idea of the marks would be helpful. Everything went fab for me except for those, I definitely made some silly errors 😫

Reply 36

Harj2807

7

Original post by Anonymouspsych

well i thought since the prize is what the player wins the -5p tells you that on average the person will lose money. I got a standard deviation of about 33.4

I’m not sure maybe you’re right. I got 33.5 for SD so same thing.

Reply 37

dfhw

9

I got 22 for C and 21 for 90th percentile? For median I got something like 17.49 or 19.49 idk.

On the last question I got something like 0.1??...

Was I supposed to find f(x) and then do the reciprocal or do the reciprocal then find f(x)?
I did the former so it might be wrong.

I got c=20 as well

Original post by jess2157

I couldn't even do that question about the prizes and that game. I guess you had to find E(X) and then find the value of the mean prize/amount paid (can't remember what it was)? I couldn't figure out to do E(X) because it said '7 or less' on one of the probabilities...

I got the same Chi-squared and hypothesis answers though.

I kinda made a new distribution, with the t values as 0, 50, 200 and 800 (the profit) and with the probabilities the same as before. Ended up getting 5p as my msan and like 33.5p as my s.d

AQA A2 Mathematics (Old Spec) - Statistics 2 MS2B - 19 June 2018 [Exam Discussion]

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