OCR (not MEI) S1 24/5 [Unofficial MS]

And can ANYONE please help me with June 2010 Q1 (iii) Q2 (iii) and all of Q8! Thankyou

Q1 (iii) is 55-14= 41
Q2 (iii) is 1/3 * 1/2 * 1 = 1/6 or you can do it as 1/3! because the three numbers can be arranged in 2! different ways

Q8: It's geometric so G(0.3)
a) P(X=4)=0.3 x 0.7^3 =0.1029 so 0.103
b) P(X<4)= 1- 0.7^3= 0.657

ii) A) Binomial and in order to have 2 viewers in 5, the last person will have to be a viewer so there must have been another viewer in the first 4 people so [4C1 x 0.3 x 0.7^3 ] x (0.3) = 0.123
B) P(X>5) so either you have no viewers in the first 5 or you have 1 viewer and need one more so [ 0.7^5] + [5C1 x 0.3 x 0.7^4 ] = 0.528

Reply 61

Nina8

8

Original post by bardsleyp

Why is the sum to infinity of a geometric series sometimes a/1-r^2 instead of a/1-r , for example june 2012 Last question ?

It isn't! Its always a/1-r but if you look at the question the ratio is (0.95)^2. Youre multiplying 0.95^2 because the clock is chiming twice, once at an hour and once every half an hour x

Reply 62

BankOfPigs

OP

12

Original post by bardsleyp

Why is the sum to infinity of a geometric series sometimes a/1-r^2 instead of a/1-r , for example june 2012 Last question ?

I did that paper as a mock.

For the specific question, you know that a = 1 / 20 since this is the change of 'success', and r is 19 / 20.
The difference between each 'half hours' (ie 0:30 -> 1:30) is r^2. And because this is specifically what you are looking for, you can change your common ratio into r^2, which allows you to use the sum to infinity to find the probability.

Reply 63

niaphonic

10

Original post by Nina8

I did it as a mock :smile:

AND no worries I get it now thankyou :biggrin:

I think the range bit threw me off, but if its possible can you post up how to do 8 (ii) still doesnt make any sense
Pm me your email and Ill send Jan '13 to you if you like

Thank you that would be great! and sure I'll post my answer to 8 (ii). Oh someone beat me to it!

Original post by bardsleyp

Why is the sum to infinity of a geometric series sometimes a/1-r^2 instead of a/1-r , for example june 2012 Last question ?

It's always a/1-r, it just happend that r = (19/20)^2 but you can also write r=0.9025

(edited 10 years ago)

Reply 64

DanielCook95

Has anyone got a link to Jan '13? Would be much appreciated!

Reply 65

purplemind

6

Original post by DanielCook95

Has anyone got a link to Jan '13? Would be much appreciated!

I only have the paper, no MS. :smile:

4732-01Jan13.pdf238.0KB

Reply 66

DanielCook95

Original post by purplemind

I only have the paper, no MS. :smile:

Thank you! :wink:

Reply 67

Nina8

8

Original post by bardsleyp

Q1 (iii) is 55-14= 41
Q2 (iii) is 1/3 * 1/2 * 1 = 1/6 or you can do it as 1/3! because the three numbers can be arranged in 2! different ways

Q8: It's geometric so G(0.3)
a) P(X=4)=0.3 x 0.7^3 =0.1029 so 0.103
b) P(X<4)= 1- 0.7^3= 0.657

ii) A) Binomial and in order to have 2 viewers in 5, the last person will have to be a viewer so there must have been another viewer in the first 4 people so [4C1 x 0.3 x 0.7^3 ] x (0.3) = 0.123
B) P(X>5) so either you have no viewers in the first 5 or you have 1 viewer and need one more so [ 0.7^5] + [5C1 x 0.3 x 0.7^4 ] = 0.528

You're a star! Thankyou :biggrin:

And last June 12 q8 part b

Reply 68

Nina8

8

Anyone? June 12 Q8 part B? Like I understand your combinations are 4 4 2 and 4 3 3 but why do you take them individually? cant it be 2 4 4 or 4 2 4 and the same for that and agh so confused :frown:

Reply 69

niaphonic

10

Original post by Nina8

Anyone? June 12 Q8 part B? Like I understand your combinations are 4 4 2 and 4 3 3 but why do you take them individually? cant it be 2 4 4 or 4 2 4 and the same for that and agh so confused :frown:

You're right! that's part of the mark scheme as well, you multiply your P(4,3,3) and P(4,4,2) each by 3, because there are 3 possible arrangements of those numbers (taking into account the double 3 and double 4).

Reply 70

aran0909

hello does anyone have the formula for standard deviation or variance in a question where i am given frequency table
thanks

Reply 71

mia_hilton

Original post by aran0909

hello does anyone have the formula for standard deviation or variance in a question where i am given frequency table
thanks

Root :sum of (x^2f / sum of f) - mean^2
Hope that helps :smile:

Reply 72

JamesWire

June 2009 - Q3

Can anyone help me explain what the vertical dotted lines between the points and the regression line represent. I kind of understand but on the mark scheme it says line given by minimum sum of squares. I'm not quite sure what this means...?

Reply 73

mia_hilton

Good luck everyone hopefully we'll be grinning in 12 hours time :smile:

Reply 74

Goods

16

Original post by JamesWire

June 2009 - Q3

Can anyone help me explain what the vertical dotted lines between the points and the regression line represent. I kind of understand but on the mark scheme it says line given by minimum sum of squares. I'm not quite sure what this means...?

The lines are the deviations from the line of best fit. The regression line is the line that minimises these deviations

Posted from TSR Mobile

Reply 75

mia_hilton

Original post by JamesWire

June 2009 - Q3

Can anyone help me explain what the vertical dotted lines between the points and the regression line represent. I kind of understand but on the mark scheme it says line given by minimum sum of squares. I'm not quite sure what this means...?

They represent least squares regression where , the least values of the difference (x and the line) are squared between each point and the regression line. (Basically the regression line rotates so that it fits with the points with the smallest sum of the differences squared) I hope that makes sense and is helpful :smile:

Reply 76

niaphonic

10

Original post by JamesWire

June 2009 - Q3

Can anyone help me explain what the vertical dotted lines between the points and the regression line represent. I kind of understand but on the mark scheme it says line given by minimum sum of squares. I'm not quite sure what this means...?

It's the line where the sum of all of the individual deviations of the points from the line are at their minimum (or to be precise, the sum of the squared deviations from the line ie. sum of squares)

Reply 77

TheMan100

9

Is anyone else hoping histograms don't come up? Or is it just me that finds them incredibly annoying?

ALSO, with regards to regression:
Say you're finding the equation of the regression line, and your value of B is something like 0.4325345954935... would you round that to 0.433? Or what?

Reply 78

bardsleyp

Guys Jan 2013 answers are on youtube with all working http://www.youtube.com/watch?v=JQU-pt2vslU

Reply 79

BankOfPigs

OP

12

Original post by TheMan100

Is anyone else hoping histograms don't come up? Or is it just me that finds them incredibly annoying?

ALSO, with regards to regression:
Say you're finding the equation of the regression line, and your value of B is something like 0.4325345954935... would you round that to 0.433? Or what?

Yes to both.

I hate all of the histograms / cumulative frequency because those 0.5 bounds are just a pain and all the questions they ask are tedious. They aren't always difficult, just as you said, 'incredibly annoying'.

For regression, when you are providing your final equation, you can round the points to 3SF. Prior to that, i highly discourage it. A misplaced rounding can screw your 'a' value as well as your 'b' so I would first write out your equation in 'full' (to like 6sf) and then round off from there, maybe even by explicitly saying '0.433 to 3sf'

Anyway, I'm going off now guys so I wish you all luck for tomorrow.

OCR (not MEI) S1 24/5 [Unofficial MS]

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