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

1. (Original post by hogree)
Because in the question it says "To the nearest minute". Thus it applies to all of the values within the class boundaries. The last one is 90.5-150.5 .

I guess the way to do it wold be instead of rounding as you say, do 0.67 + (14/31)*1 . But I do believe you're right. I think Interpolation is not necessary and we are able to round the nearest value.

That's right but that's ONLY TRUE when the events are independent. After all, if you think of, if A and B are independent. A|B (A given B) is basically asking for A since there's no link in independent events.
Ahhh right okay cool. So is everything on a tree diagram independent of each other?
2. can someone PLEASE clear up coding, i get so confused when they ask to use it in questions including Sxx Sxy Syy and regression
3. (Original post by Siddhart1998)
Thanks except there is nothing on "whiskers" in the textbook hence why I was asking aha
the min/max/outlier all belong on whiskers... so yh you do need to learn it... aha
4. (Original post by clairesullive)
can someone PLEASE clear up coding, i get so confused when they ask to use it in questions including Sxx Sxy Syy and regression
Is there a particular question that you find hard? One thing to remember that PMCC never changes with coding. Dont know if this helps?

(Original post by Siddhart1998)
Ahhh right okay cool. So is everything on a tree diagram independent of each other?
Nope. Tree Diagrams arent always independent. So flipping a coin would be an independent event, since the second flip doesn't change dependent on the first flip. But boys and girls cycling to school would be dependent as the odds for cycling would go up, say, if you were a girl in comparison to if you were a boy.
5. (Original post by tazza ma razza)
the min/max/outlier all belong on whiskers... so yh you do need to learn it... aha
Thanks 😘
6. (Original post by hogree)
Is there a particular question that you find hard? One thing to remember that PMCC never changes with coding. Dont know if this helps?
Thanks so much!! i know mean changes with coding completely, where as Variance and SD only change with multiplying or dividing but what about the quartiles & IQR?
And i just can't get my head around how, for example I use coding to find the equation of a new regression line for example
7. Hardest paper?
8. (Original post by clairesullive)
Thanks so much!! i know mean changes with coding completely, where as Variance and SD only change with multiplying or dividing but what about the quartiles & IQR?
And i just can't get my head around how, for example I use coding to find the equation of a new regression line for example
Something useful on Coding for Sxx and Sxy and Syy:
If you add a fixed amount to either the x or y values you will not affect any of Sxx Sxy or Syy because they all subtract the mean.
If you multiply the x values by say 2 you will quadruple the Sxx value, double the Sxy value and not change the Syy value.

Here's an example on Regression:
A long distance lorry driver recorded the distance travelled, m miles, and the amount of fuel
used, f litres, each day. Summarised below are data from the driver’s records for a random
sample of 8 days.
The data are coded such that x = m – 250 and y = f – 100.
x = 130 y = 48 xy = 8880 Sxx = 20 487.5

(a) Find the equation of the regression line of y on x in the form y = a + bx.

(b) Hence find the equation of the regression line of f on m.

Answer for A) Whatever it is, using the values you have. End with y = a + bx
B) Replace your y = a + bx with (f-100) = a + b (m-250)

Actually not sure about Quartiles coding, do you know whether you've got a Question on that?
9. remember chapter 1
10. Anyone please help with part b? It says the fastest 30%, so why in the markscheme is it then looking for P(X<x) = 0.3, instead of P(X>x) = 0.3?

Many thanks!

Zacken SeanFM
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11. (Original post by hogree)
Something useful on Coding for Sxx and Sxy and Syy:
If you add a fixed amount to either the x or y values you will not affect any of Sxx Sxy or Syy because they all subtract the mean.
If you multiply the x values by say 2 you will quadruple the Sxx value, double the Sxy value and not change the Syy value.

Here's an example on Regression:
A long distance lorry driver recorded the distance travelled, m miles, and the amount of fuel
used, f litres, each day. Summarised below are data from the driver’s records for a random
sample of 8 days.
The data are coded such that x = m – 250 and y = f – 100.
x = 130 y = 48 xy = 8880 Sxx = 20 487.5

(a) Find the equation of the regression line of y on x in the form y = a + bx.

(b) Hence find the equation of the regression line of f on m.

Answer for A) Whatever it is, using the values you have. End with y = a + bx
B) Replace your y = a + bx with (f-100) = a + b (m-250)

Actually not sure about Quartiles coding, do you know whether you've got a Question on that?
You're a life saver! Thank you so so so much! Ahhh so if i multiplied the y values by for example 3 i would multiply the value of Syy by 9, triple the Sxy and not change the Sxx?
And i mean if they ask you 'state what would happen if 2 more people joined the competition on the values of Q1, Q2,Q3 , interquartile range and the range?' which would be affected like which values would increase and what not etc
12. When we are dealing with discrete uniform distribution and trying to find the expected value with n+1/2, is n the number of values or the largest value in the table?
13. (Original post by iMacJack)
Anyone please help with part b? It says the fastest 30%, so why in the markscheme is it then looking for P(X<x) = 0.3, instead of P(X>x) = 0.3?

Many thanks!

Zacken SeanFM
If you think about it, the fastest 30% will have the lowest 30% times. So that's why you're looking for Less Than.
14. (Original post by hogree)
If you think about it, the fastest 30% will have the lowest 30% times. So that's why you're looking for Less Than.
Oh yeah!! Because the fastest times will be lower than the mean! How silly! That is very cheeky. Thank you
15. Any really hard papers?
16. (Original post by clairesullive)
You're a life saver! Thank you so so so much! Ahhh so if i multiplied the y values by for example 3 i would multiply the value of Syy by 9, triple the Sxy and not change the Sxx?And i mean if they ask you 'state what would happen if 2 more people joined the competition on the values of Q1, Q2,Q3 , interquartile range and the range?' which would be affected like which values would increase and what not etc
I believe that's true yeah about the y. It seems like the logical route anyway.I don't think I've seen a question like that before, but if it does pop up, the Range won't be changed unless the two values are bigger/smaller than the previous Minimum& Maximum.As for the Quartiles and InterQuartile Range, I really doubt they're going to ask you to add in values without already giving you the values previously. I haven't seen it. If you already have a list of values, just add in the "new values" and recalculate I guess. But I've only seen Coding appear in Mean, Variance, Discrete Random Variables, PMCC and Regression.
17. (Original post by hogree)
I believe that's true yeah about the y. It seems like the logical route anyway.I don't think I've seen a question like that before, but if it does pop up, the Range won't be changed unless the two values are bigger/smaller than the previous Minimum& Maximum.As for the Quartiles and InterQuartile Range, I really doubt they're going to ask you to add in values without already giving you the values previously. I haven't seen it. If you already have a list of values, just add in the "new values" and recalculate I guess. But I've only seen Coding appear in Mean, Variance, Discrete Random Variables, PMCC and Regression.
I mean discrete random variables sorry!
18. (Original post by clairesullive)
I mean discrete random variables sorry!
So in Discrete Random Variables, all you'll have to do is to Code the Expectation and Variance. Just remember the Rule that

E(aX+B) = aE(X) + b
Var(aX+B) = a² Var(X)
19. (Original post by hogree)
So in Discrete Random Variables, all you'll have to do is to Code the Expectation and Variance. Just remember the Rule that

E(aX+B) = aE(X) + b
Var(aX+B) = a² Var(X)
Ah you're amazing thank you so much
you'll do great on that exam tomorrow! Good luck and thanks once more
20. When doing histograms and stuff. For calculating the width of the bars or for like area of the bars. Do you always go +/-0.5 of the two boundary numbers ( e.g. bar goes from 5 to 10 on the x-axis, so you take width to be 6 and not 5 as its 4.5-10.5). I am just confused by this (when do it) as in some questions you do it and some you don't.

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