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1. (Original post by Zacken)
"Given that it is 127 hours since Alice last charged her phone" means that it's been at least 127 hours since Alive charged her phone throughout the journey. So it could be anywhere between 127 hours and infinity hours since she last charged her phone.
Gotcha, thanks.
2. For working out the variance of question 2(a) of this paper, I used the formula of the standard deviation squared to work it out, however the model answers uses Sxx/n. Why did they use that?

Model Paper: https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf
3. (Original post by Glavien)
For working out the variance of question 2(a) of this paper, I used the formula of the standard deviation squared to work it out, however the model answers uses Sxx/n. Why did they use that?

Model Paper: https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf
Think about the definition of Sxx in terms of summations and how it compares to the formula of variance in terms of summations.

I'd use the normal formula tbh.
4. (Original post by Zacken)
Think about the definition of Sxx in terms of summations and how it compares to the formula of variance in terms of summations.

I'd use the normal formula tbh.
Ahhh, yeah I understand it now, thanks. Whats the 'normal formula'?
5. (Original post by Glavien)
Ahhh, yeah I understand it now, thanks. Whats the 'normal formula'?
The one that you used.
6. (Original post by Zacken)
The one that you used.
Cool, thanks!
7. (Original post by Glavien)
Cool, thanks!
No problem.
8. What is the best way of representing the information for question 7 in order to make the question clearer, tree diagram or venn diagram? I don't understand how you can work out P(LH intersection F) for part (b).

Paper: https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf
9. (Original post by Glavien)
What is the best way of representing the information for question 7 in order to make the question clearer, tree diagram or venn diagram? I don't understand how you can work out P(LH intersection F) for part (b).

Paper: https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf
Tree-diagram.
10. Can you explain question 7(f) of this question please? I'm really confused, I understand the P(S=1) = 0.2 but don't know what to do next.

Paper: https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf
11. (Original post by Glavien)
Can you explain question 7(f) of this question please? I'm really confused, I understand the P(S=1) = 0.2 but don't know what to do next.

Paper: https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf
It's just saying "what is the probability that the score on the first die is 1 and the score on the second die multiplied by the score on the first die is less than 5).

So that's P(S1 = 1 and S2 = 1) + P(S1 = 1 and S2 =2) + P(S1 = 1 and S2 = 3) + P(S1 = 1 and S2 = 4)

since in all those cases, S1 = 1 and S1 * S2 < 5.

Then remember that P(S1 = 1 and S2 = 1) = P(S1=1) * P(S2 = 1) and the same for the others.
12. (Original post by Zacken)
It's just saying "what is the probability that the score on the first die is 1 and the score on the second die multiplied by the score on the first die is less than 5).

So that's P(S1 = 1 and S2 = 1) + P(S1 = 1 and S2 =2) + P(S1 = 1 and S2 = 3) + P(S1 = 1 and S2 = 4)

since in all those cases, S1 = 1 and S1 * S2 < 5.

Then remember that P(S1 = 1 and S2 = 1) = P(S1=1) * P(S2 = 1) and the same for the others.
Thanks, what do the curly braces mean when stating S1=1?

Also, could the question be written as:

If S1 = 1 show that P(X<5) = 0.16
13. For question 3(e) of this paper, would you work out the number of plants with a yield above (mean + standard deviation)? How would you do that as it the frequency somewhere in between the interval 15<=y<35 plus 4?

Paper: https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf
14. (Original post by Glavien)
Thanks, what do the curly braces mean when stating S1=1?
Just some technical stuff about events and sets, doesn't really mean anything in particular.

Also, could the question be written as:

If S1 = 1 show that P(X<5) = 0.16
I think so.

(Original post by Glavien)
For question 3(e) of this paper, would you work out the number of plants with a yield above (mean + standard deviation)? How would you do that as it the frequency somewhere in between the interval 15<=y<35 plus 4?

Paper: https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf
Have a look at this.
15. (Original post by Zacken)
Just some technical stuff about events and sets, doesn't really mean anything in particular.

I think so.

Have a look at this.
Thanks!
16. For question 2(e)(iii), I would've thought when using the standard deviation formula the term sum(x^2f) would increase, as the value 7.88km is in the interval 6-10 so the midpoint used would be 8 and the frequency used is 11. Also the sum(f) will increase to 51. Thus, the standard deviation increasing. Can you please explain why this is not the case? Thanks!

Paper: https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf
17. (Original post by Glavien)
For question 2(e)(iii), I would've thought when using the standard deviation formula the term sum(x^2f) would increase, as the value 7.88km is in the interval 6-10 so the midpoint used would be 8 and the frequency used is 11. Also the sum(f) will increase to 51. Thus, the standard deviation increasing. Can you please explain why this is not the case? Thanks!

Paper: https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf
You're overcomplicating this. She travels an exact distance of the mean. This means that she contributes nothing to the standard deviation or variance. Remember that variance is sum of (x - mean)^2 or something, in her case x = mean so her part of the sum is mean - mean = 0.
18. (Original post by Zacken)
You're overcomplicating this. She travels an exact distance of the mean. This means that she contributes nothing to the standard deviation or variance. Remember that variance is sum of (x - mean)^2 or something, in her case x = mean so her part of the sum is mean - mean = 0.
Yeah, I always tend to overthink things. Thanks for explaining it too me.
19. (Original post by Glavien)
Yeah, I always tend to overthink things. Thanks for explaining it too me.
No problem.
20. For question 1(d), why is it incorrect to do this:

2*P(1and3) + 2*P(3and5) + 2*P(5and1)

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

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