Need some help guys I really don't think I'm doing this right
right now I have:
a. p(x=3)
20!/3!1! (.05)^3 (.95)^17 = .24
b. p (x > 19) = p(x=19) + p(x=20) = .27
c. Mx = 1 s.d.= .97
Sorry about notation differences. It happens.
Pr(3) = p(x=3)
You have the right idea, but something is going whacky.
In part a, you have a 1! in the denominator where there should be a 17! Even so, what you have written comes nowhere near 0.24. Must be more arithmetic errors going on. [(20*19*18)/(3*2)]*(0.05^3)*(0.95^17) = 0.0596 or so.
In part b, that probability is WAY to big. I'm thinking maybe you made the same kind of denominator error.
20*(.05^19)*0.95 + 0.05^20 is a very small number.
Good call on Part c.