Edexcel S1 - 15th June, 2016 [Exam Discussion]

OP

Can anyone explain how to work quartiles (median, lower quartile and upper quartile)?

For example how is the process different for discrete and continuous data?
When to use n and when to use n+1?
When to round, not round, or find the midpoint between two values?

Reply 241

Exavior

2

Original post by GarlicBread01

Can anyone explain how to work quartiles (median, lower quartile and upper quartile)?

For example how is the process different for discrete and continuous data?
When to use n and when to use n+1?
When to round, not round, or find the midpoint between two values?

For discrete you can use n/2 for median. If it is not a whole number round up. If it is a whole number then the median would be midway between this turn and the term above it. This is the same for quartiles. There is no rule having to use n/2 and n+1\2, you can use either. It is just that there is a different rule for n+1/2 when the answer is a whole number (you may aswell just learn how to use the n/2 and forget about the other or vise versa.

For contiuous data you just use n/2 and don't round and use interpolation to find the median and quartiles.

Reply 242

Philip-flop

18

So this is the first time I've come across a question like this! Can someone please explain it to me?...
Click to enlarge...
S1 June 2014 Q2.png

Reply 243

4nonymous

11

Original post by Philip-flop

So this is the first time I've come across a question like this! Can someone please explain it to me?...
Click to enlarge...
S1 June 2014 Q2.png

Just put the values of y into the equation and solve for x
so
60.8=1.4x-20
x=60.8+20/1.4=57.7

then do the same for s.d but remember that the -20 doesn't have an effect on it.

If you're still confused I suggest you look on exam solutions he explains it well.

Reply 244

physicsamor

20

I hope we don't get a paper like the June 2015 otherwise I'm failing. Every other paper has been good for me except the 2015 which I scored terribly in 😐

Reply 245

Aliceeee12

2

Original post by siamesedaffodil

sd is affected by only multiplication/division
mean is affected by multiplication, division, addition and subtraction

standard deviation measures how spread out data is from the mean.

logically, if you added 10 to each piece of data, the standard deviation would stay the same as each point would move 10 places and the distance between them would stay the same. so standard deviation is not affected by addition/subtraction. however, standard deviation IS affected by multiplication/division. Think of transforming graphs-- when you add or subtract 2 from a graph, all points move 2 places. if you multiplied a graph by 2, the graph is stretched and the distance between each point has changed. in the same way, standard deviation is affected by multiplication/division

as for the mean...it is a measure of location and is affected by ALL coding.

Thankyou so much!

Reply 246

hogree

15

Original post by GarlicBread01

Can anyone explain how to work quartiles (median, lower quartile and upper quartile)?

For example how is the process different for discrete and continuous data?
When to use n and when to use n+1?
When to round, not round, or find the midpoint between two values?

Quote I found. Also find this tricky. Would like if someone could confirm this?

Original post by Lou Reed

For the new Edexcel syllabus...For Continuous data (grouped frequency tables, histograms etc.)

Median:n/2 and use linear interpolation

Quartiles:n/4 or 3n/4 and use linear interpolation

Linear Interpolation:m + cw[(X-fc)/f]where m = minimum boundary of the class that X is incw = class width of the class that X is inX = n/2 for median, n/4 for lower quartile, 3n/4 for upper quartilen = total number in the samplefc = cumulative frequency of the classes below the class that X is inf = frequency of the class that X is in

For Discrete data (stem and leaf, listed data etc, frequency tables)

Median: (n+1)/2 and pick that value, if it is a .5 then take average of the two values above and below it (e.g. if (n+1)/2 = 50 then pick the 50th value, if (n+1)/2 = 50.5 then average the 50th and 51st values)

Quartiles:n/4 or 3n/4 and round UP and pick that value. If n/4 or 3n/4 is an integer, then take average of that value and the one above it (e.g. if n/4 = 25, then take average of 25th and 26th values).

(edited 7 years ago)

Reply 247

wkaren

Original post by hogree

Quote I found. Also find this tricky. Would like if someone could confirm this?

Best way:

Never use n+1. LQ n+1/4 Median n/2 and UQ 3n/4

Discrete data, if you get an integer then your answer is the average of this number and the one above, if it is a decimal answer then you round up to the next number.

Example - 10 terms. LQ = 10/4 = 2.5 = 3rd number, 10/2 = 5 = average of 5th and 6th number. 10/4*3 = 7.5 = 8th number.

Continuous data LQ n+1/4 Median n/2 and UQ 3n/4 then interpolate

Reply 248

wkaren

Original post by wkaren

Best way:

Never use n+1. LQ n+1/4 Median n/2 and UQ 3n/4

Discrete data, if you get an integer then your answer is the average of this number and the one above, if it is a decimal answer then you round up to the next number.

Example - 10 terms. LQ = 10/4 = 2.5 = 3rd number, 10/2 = 5 = average of 5th and 6th number. 10/4*3 = 7.5 = 8th number.

Continuous data LQ n+1/4 Median n/2 and UQ 3n/4 then interpolate

Sorry first line should say:

Never use n+1. LQ n/4 Median n/2 and UQ 3n/4

Reply 249

hogree

15

Original post by wkaren

Sorry first line should say:

Never use n+1. LQ n/4 Median n/2 and UQ 3n/4

Makes sense. Thanks for clearing that up. :smile:

Reply 250

kkboyk

21

Original post by physicsamor

I hope we don't get a paper like the June 2015 otherwise I'm failing. Every other paper has been good for me except the 2015 which I scored terribly in 😐

What made you do badly on June 2015 paper?

Reply 251

physicsamor

20

Original post by kkboyk

What made you do badly on June 2015 paper?

I feel like just giving up with S1, that paper gave me a panic attack. It was question 5 and question 6 and a mistake with the venn diagram (but at least I understand where i went wrong)

Especially with question 6 iii and 6 iiv and 6B
And just 5 in general (but more of the wording) I've tried looking at Ma, ms and videos but I just couldn't understand.

Oh well.

Reply 252

Philip-flop

18

Why is it with Edexcel past papers (including C1, C2, S1 etc) they progressively get more difficult each year? e.g. June 2007 is so much easier in comparison to June 2015!!

Reply 253

physicsamor

20

Original post by Philip-flop

Why is it with Edexcel past papers (including C1, C2, S1 etc) they progressively get more difficult each year? e.g. June 2007 is so much easier in comparison to June 2015!!

It's annoying, they want me to fail :redface:

Reply 254

KloppOClock

14

Quick question, if for my answer i have given the correct answer then underneath I have written the answer to 3.s.f wrongly. would I get the A1 for my first answer as the mark scheme states answers which round to that or would they see my incorrect answer after my correct answer and lose the mark. basically do they ignore subsequent marking once you get your answer?

Reply 255

T17MA

2

How confident are you guys with s1?
I feel as if I'm going to mess this up.

Posted from TSR Mobile

Reply 256

KloppOClock

14

Original post by T17MA

How confident are you guys with s1?
I feel as if I'm going to mess this up.

Posted from TSR Mobile

same, i keep making the same mistakes even tho i have enough time to check my questions three times over

Reply 257

LittleBoxes

16

I'm really bad at probability. Really bad. Any tips? :s-smilie:

Reply 258

kkboyk

21

Original post by LittleBoxes

I'm really bad at probability. Really bad. Any tips? :s-smilie:

Watch these tutorial videos (or go through your textbook again, and if struggling keep asking questions here or to your teacher), and do the Probability past paper question booklet from Physics and Maths Tutor.

Original post by T17MA

How confident are you guys with s1?
I feel as if I'm going to mess this up.

Posted from TSR Mobile

Feel a bit meh. I need to get more than 90% and I don't really have the motivation. S1 is too boring and very wordy.

Original post by physicsamor

I feel like just giving up with S1, that paper gave me a panic attack. It was question 5 and question 6 and a mistake with the venn diagram (but at least I understand where i went wrong)

Especially with question 6 iii and 6 iiv and 6B
And just 5 in general (but more of the wording) I've tried looking at Ma, ms and videos but I just couldn't understand.

Oh well.

I struggled with the very same questions when I was doing it as a mock on Friday. Keep practicing in these particular questions to make you feel more confident.