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

1. Can someone explain why sometimes you used n+1/2 and sometimes n/2 for the median. Which one do I use and where.

Anyone have tips on how to not make stupid mistakes. I am scared ill make a stupid mistake part a and carry it through to part f. ;(

I need to get at least 65 to make sure I have a solid A. I got 60/75 for C1 and 70/75 for C2
2. Guys, in the normal distribution questions, how are we supposed to know exactly what value of z to take when given probabilities?

For example, say I was given that the probability of getting less than a certain value X is 0.95. So I go to the table to find out what value of z will give a probability of 0.95, but the closest z values you can get are 1.64 and 1.65, which give probabilities of 0.9495 and 0.9505, respectively. I had no clue how I was supposed to choose between the two, so I just went with 1.65.

In the mark scheme, however, it specifically says that if I use 1.65, I lose a mark. This caused me to then lose another mark in the next part of the question.

So is there any way to know which one I should choose? In situations like this, do I just go with the lower z value?
3. (Original post by Dohaeris)
Guys, in the normal distribution questions, how are we supposed to know exactly what value of z to take when given probabilities?

For example, say I was given that the probability of getting less than a certain value X is 0.95. So I go to the table to find out what value of z will give a probability of 0.95, but the closest z values you can get are 1.64 and 1.65, which give probabilities of 0.9495 and 0.9505, respectively. I had no clue how I was supposed to choose between the two, so I just went with 1.65.

In the mark scheme, however, it specifically says that if I use 1.65, I lose a mark. This caused me to then lose another mark in the next part of the question.

So is there any way to know which one I should choose? In situations like this, do I just go with the lower z value?

You would have to choose 1.64 because 0.9495 rounds up to 0.950 (3dp) whereas if you round up 1.65 it goes to 0.951(3dp) so its better to look at it like that and choose 1.64 as the answer to use.
4. (Original post by 4nonymous)
You would have to choose 1.64 because 0.9495 rounds up to 0.950 (3dp) whereas if you round up 1.65 it goes to 0.951(3dp) so its better to look at it like that and choose 1.64 as the answer to use.
That makes sense. So if I wanted a value of z, I would choose whichever gave the closest probability to the one I wanted. And if they're equal, like 1.64 and 1.65, just round it. Thanks
5. (Original post by Dohaeris)
That makes sense. So if I wanted a value of z, I would choose whichever gave the closest probability to the one I wanted. And if they're equal, like 1.64 and 1.65, just round it. Thanks
Yes just keep rounding it till you get an answer which is closest to the one you need. In this case it is 1.64
6. (Original post by mahmzo)
Can someone explain why sometimes you used n+1/2 and sometimes n/2 for the median. Which one do I use and where.

Anyone have tips on how to not make stupid mistakes. I am scared ill make a stupid mistake part a and carry it through to part f. ;(

I need to get at least 65 to make sure I have a solid A. I got 60/75 for C1 and 70/75 for C2
That confuses me too, I hope this will help
Also I think you get carry through marks so you can't be marked down for the same mistake twice which is good, I think they just re-calculate with the 'wrong' previous answer so don't worry. It's what my stats teacher does but correct me if I'm wrong.
7. does anyone know if we have to clear the memory from our graphical calculators before every exam or is just once enough for the whole exam period?
8. (Original post by andy135)
does anyone know if we have to clear the memory from our graphical calculators before every exam or is just once enough for the whole exam period?
Every exam

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9. (Original post by andy135)
does anyone know if we have to clear the memory from our graphical calculators before every exam or is just once enough for the whole exam period?
Graphical calculators are banned for this exam?
10. (Original post by imran_)
Graphical calculators are banned for this exam?
I'm doing AQA stats 1 where we're allowed graphical calculators but i couldn't find a thread for the aqa one
11. (Original post by mahmzo)
Can someone explain why sometimes you used n+1/2 and sometimes n/2 for the median. Which one do I use and where.

Anyone have tips on how to not make stupid mistakes. I am scared ill make a stupid mistake part a and carry it through to part f. ;(

I need to get at least 65 to make sure I have a solid A. I got 60/75 for C1 and 70/75 for C2

depends on the type of data, whether it is discrete etc. however in mark schemes you get the marks if you do it either way
12. Can someone pls help me with q 5 d) and e)

https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf
Attached Images

13. https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf

hi for question 7c, I dont get why they did 1-0.9545
I would have thought it would be 1-0.0618 as >188 would be on the right side of the normal distribution sketch
14. Attachment 545745545747Hi, For both these questions from Jan 2011 8 b and c I don't understand where the -2.3623 came from or the -1.2816. How did they get this from 0.90 and 0.99 because in the stats tables they done match up? Thank you!
Attached Images

15. (Original post by KloppOClock)
depends on the type of data, whether it is discrete etc. however in mark schemes you get the marks if you do it either way
Exam solutions says do n+1/2 all the time.
16. Anyone else sitting the IAL paper?
17. (Original post by mahmzo)
Exam solutions says do n+1/2 all the time.
sure but in actuality it depends on the type of data, mark schemes will allow either way however.
18. Anyone know where I can get hold of good worked examples and questions for practicing Conditional Probabilities? e.g. P(AnB), P(AuB). This is the area that I seem to struggle with the most especially when trying to figure out what region of a venn diagram needs to be shaded for something more difficult e.g. P(AuB'.
19. (Original post by Philip-flop)
Anyone know where I can get hold of good worked examples and questions for practicing Conditional Probabilities? e.g. P(AnB), P(AuB). This is the area that I seem to struggle with the most especially when trying to figure out what region of a venn diagram needs to be shaded for something more difficult e.g. P(AuB'.
Look at exam solutions tutorials. He also has some practice questions which he explains how to do.
20. okay i literally remember nothing of this moduls, i have 7 days to learn it. Where do I start, questions by topic, just straight into past papers?

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