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1. ### Binomial Probability problem.

Actually, this could be a Geometric distribution problem right? In that case we would sum x from 5 to 25 of (.1)(.9)^(x-1). This gives 0.5843102
2. ### Binomial Probability problem.

Would we not express each of those via Bin(n,.1) where x=1? If not, how would we express one of them? Thanks
3. ### Binomial Probability problem.

Homework Statement 10% of engines manufactured on an assembly line are defective. If engines are randomly selected one at a time and tested, what is the probability that the first defective engine will be found between the 5th trial and the 25th trial, inclusive? Homework Equations...
4. ### Derivative of (1+e^-x)^-1

Of course, silly me. So I get (e^(-x))((1+e^-x)^-2) Can this be simplified? -Cheers
5. ### Derivative of (1+e^-x)^-1

Homework Statement Find the derivative of (1+e^-x)^-1 Homework Equations The Attempt at a Solution I can't seem to get anywhere with this. Should I be looking for a property of something like the cosh function to apply to this? Thanks
6. ### Simple Probability Proof

So what you're saying is that I have to show that A is a subset of AUB. This is done by definition that AUB=A+B therefore A is a subset of AUB and it follows (as you said) that P(A) is less than or equal to P(AUB). Correct? What would I do to prove the intersection is less than A? cheers
7. ### Simple Probability Proof

Homework Statement Prove the following: P(A∩B) ≤ P(A) ≤ P(AUB) Homework Equations The Attempt at a Solution I first attempt to show that P(A) is a subset of P(AUB) which therefore means it is ≤ P(AUB): P(AUB)=P(A)+P(B)-P(A∩B), thus P(A) is a subset of P(AUB)...I think that...