Binomial Thereom (S1 or P3) Watch

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Elle
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I know this is an easy question but I keep getting it wrong..

What do n and r stand for in the formulae nCr for the Binomial Thereom?
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Nima
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(Original post by Elle)
I know this is an easy question but I keep getting it wrong..

What do n and r stand for in the formulae nCr for the Binomial Thereom?
not doing Stats, havent got to P3 yet, sorry!
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Elle
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(Original post by bono)
not doing Stats, havent got to P3 yet, sorry!
thats ok .. anyone else?
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Nima
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(Original post by Elle)
thats ok .. anyone else?
ask ollie and leekey, they r older than me so they will have done it.

ollie is doing engineering at uni so he must know this stuff.
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Ollie
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(Original post by Elle)
I know this is an easy question but I keep getting it wrong..

What do n and r stand for in the formulae nCr for the Binomial Thereom?
we dont do this at uni i dont think but from what i remember ncr works out the multiplyer in the polynomial. eg. in (x+1)^3 would be x^3 +3x^2+3x+1 and you could have worked each mulitplyer by putting 3nCr1 for x^3, 3ncr2 for the 3x^2. you see? it justs give you the number to go infront of the x bit.
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Nima
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(Original post by Ollie)
we dont do this at uni i dont think but from what i remember ncr works out the multiplyer in the polynomial. eg. in (x+1)^3 would be x^3 +3x^2+3x+1 and you could have worked each mulitplyer by putting 3nCr1 for x^3, 3ncr2 for the 3x^2. you see? it justs give you the number to go infront of the x bit.
the brain!!
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Elle
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(Original post by Ollie)
we dont do this at uni i dont think but from what i remember ncr works out the multiplyer in the polynomial. eg. in (x+1)^3 would be x^3 +3x^2+3x+1 and you could have worked each mulitplyer by putting 3nCr1 for x^3, 3ncr2 for the 3x^2. you see? it justs give you the number to go infront of the x bit.
Thanks Ollie.. I think I get it.. kind of
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hornblower
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(Original post by Elle)
I know this is an easy question but I keep getting it wrong..

What do n and r stand for in the formulae nCr for the Binomial Thereom?
I guess you already know what the nCr button does - it works out coefficients. Anyway, in the binomial expansion of (1 + x)^n

n is the power to which the binomial is raised to.

r is the power to which x is raised to.

Remember, nCr = n! / r!(n - r!)

We did this in P2 by the way.

J.
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meepmeep
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(Original post by Elle)
I know this is an easy question but I keep getting it wrong..

What do n and r stand for in the formulae nCr for the Binomial Thereom?
It gives the number of ways you can choose r things from a group of n things. (from the statistics perspective)

eg 8C0 is 1 because there is only one way to pick nothing from 8.
8C1 is 8 because there are 8 ways you can pick...
and so on
The formula is: n!/r!(n-r)!
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Elle
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Is n!/r!(n-r)! the shortened version of another formulae? Because in my textbook there is a longer version with p^y P^(y-1) at the end of it..
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meepmeep
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(Original post by Elle)
Is n!/r!(n-r)! the shortened version of another formulae? Because in my textbook there is a longer version with p^y P^(y-1) at the end of it..
The formula for the probability of picking this result is:
nCr P(x)^r P(x')^(n-r)

where P(x) is the probability of a result.

The nCr bit is in the formula so the n!/(r!(n-r)! bit is in.
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Elle
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(Original post by meepmeep)
The formula for the probability of picking this result is:
nCr P(x)^r P(x')^(n-r)

where P(x) is the probability of a result.

The nCr bit is in the formula so the n!/(r!(n-r)! bit is in.
cool.. lol, I'm finally getting it! thanks
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hornblower
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(Original post by Elle)
Is n!/r!(n-r)! the shortened version of another formulae? Because in my textbook there is a longer version with p^y P^(y-1) at the end of it..
n! means n factorial

For example,
1! = 1
2! = 1 * 2 = 2
3! = 1 * 2 * 3 = 6
(n - 1)! = 1 * 2 * 3 * 4 ... * (n - 1)
n! = 1 * 2 * 3 * 4 ... * (n - 1) * n

Most calculators stop at 69!

J.
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