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Evaluate E(X) of F(x) = kx^3 S1 Urgent! Tweet

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1. Evaluate E(X) of F(x) = kx^3 S1 Urgent!
Hi there,

If it already gives me the function F(x)=kx^3 and it asks to Evaluate E(X) I thought all I do is integrate F(x) * x dx, but in the mark scheme it says that I must first differentiate F(x) first, why is this?

Is it to get F(x) to f(x)? And if so is this standard for all E(X) questions?
2. Re: Evaluate E(X) of F(x) = kx^3 S1 Urgent!
FX gives you the sum of the probability so that when x equals 3 you are finding the probability for x is smaller than and equal to 3. fx gives you the probability for that specific value
3. Re: Evaluate E(X) of F(x) = kx^3 S1 Urgent!
Ok thanks!
4. Re: Evaluate E(X) of F(x) = kx^3 S1 Urgent!
(Original post by elitelight)
FX gives you the sum of the probability so that when x equals 3 you are finding the probability for x is smaller than and equal to 3. fx gives you the probability for that specific value
(Original post by Ryan44)
Ok thanks!
Wouldn't normally do this but I have to correct you. f(x) does not give the probability for that specific value, since this is a continuous probability distribution. f(x) is the probability density function.