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# Maths Help watch

1. How do i use STANDARD DEVIATION?
2. (Original post by Naz1)
How do i use STANDARD DEVIATION?
I know the formula but it's too difficult to write it out on here. I say you go and find it your self.
3. (Original post by Naz1)
How do i use STANDARD DEVIATION?
s = sq.root something or other from the ol S1. Thank god i do mechanics.
4. (Original post by Sahir)
s = sq.root something or other from the ol S1. Thank god i do mechanics.
Square root of the variance, I think.
5. Gaah, I forget, there are three variations and I mix them up. Square root of the variance it is, shouldn't it be in any textbook or revision website...
6. sq. root of -b+ 4ac
2a

check it in a formula bk though.
a = f1st part of equation (x^2 part)
b = 2nd part of equation (x part)
c = 3rd part of equation (no. part)

Woek it out bit by bit if you need to rather than all at once and mesing the order up.
7. Standard Deviation
= the square root of :

(Sigma x squared
divided by n

then minus the mean squared.)

Where sigma x sqaured is all your different values squared and added up

and n is the number of values you have
8. (Original post by Pi^3)
sq. root of -b+ 4ac
2a

check it in a formula bk though.
a = f1st part of equation (x^2 part)
b = 2nd part of equation (x part)
c = 3rd part of equation (no. part)

Woek it out bit by bit if you need to rather than all at once and mesing the order up.
mmm that looks more like the quadratic formula
9. (the thing about standard deviation that I wish someone had told be years before)

66% of your values will be within the band of the mean + and - one * SD

95% will be within plus or minus 2SDs from the mean

99% will be within 3SDs of the mean

So for an experiment the SD essentially gives you the margin of error - most people use 2SD for this purpose.

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