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# S1 formulas Edexcel Watch

1. What are all the formulas that aren't given on the data sheet, Ive looked online for one but they all seem to leave out interpolation..?
2. (Original post by LeilaCCG)
What are all the formulas that aren't given on the data sheet, Ive looked online for one but they all seem to leave out interpolation..?
The main one that's worth knowing is the one for calculating variance and standard deviation.

There is a formula for interpolation, but the 'ratio' method seems to be getting more popular, e.g. for the median

Cumulative frequencies 50, 55, 70 (55th value is the one for the median)
Class boundaries 10, Q2, 20 (where Q2 is how far you go into the class for the median)

(Q2-10)/(20-10) = (55-50)/(70-50) and solve for Q2.
3. (Original post by M.C. Math)
The main one that's worth knowing is the one for calculating variance and standard deviation.
It's given in the formula booklet though.
4. (Original post by Zacken)
It's given in the formula booklet though.
Hi. I've checked the formulae booklets for AQA, Edxcel, OCR and OCR MEI and only the expectation and variance formulae are given (for discrete random variables).
5. (Original post by M.C. Math)
Hi. I've checked the formulae booklets for AQA, Edxcel, OCR and OCR MEI and only the expectation and variance formulae are given (for discrete random variables).
Yep, and all you need to do is take where is the number of thingies you have. After all, your data is discrete and uniform.

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