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Poisson - find r

Hi,

Given that lambda = 2.1 and P(X=r)=0.1890, find the value of r.

I don't know how to isolate r, mainly because of the r! term involved. Can someone please show me how this is done.

Thanks.
Reply 1
Avatar for BabyMaths
BabyMaths
Original post by MonsterFromTheId
Hi,

Given that lambda = 2.1 and P(X=r)=0.1890, find the value of r.

I don't know how to isolate r, mainly because of the r! term involved. Can someone please show me how this is done.

Thanks.


Just try a few values. It won't take long.
Reply 2
Avatar for Llewellyn
Llewellyn
14
Original post by MonsterFromTheId
Hi,

Given that lambda = 2.1 and P(X=r)=0.1890, find the value of r.

I don't know how to isolate r, mainly because of the r! term involved. Can someone please show me how this is done.

Thanks.

Because the probability is not rational (e^(-2.1) is not rational, so the probability is not rational) the only way to do this is just by trying values for r. (0.1890 is just an approximation so you cannot really solve for r).

0.189 is a reasonably high probability. And if lambda is 2.1 you should be excepting a number near-ish 2 :smile:
Thanks for the help guys, I appreciate it. :smile:
Reply 4
Avatar for Dedly13
Dedly13
Have you considered using the table function on the calculator?


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