# are you sure??? or am I wrong again???

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Posted by T.Gracken on September 23, 2002 at 19:18:37:

In Reply to: Re: smoker population posted by Soroban on September 23, 2002 at 13:25:05:

: : Suppose that the population of a certain city is 40% male and 60% female. Suppose also that 50% of the males and 30% of the females smoke. Find the probablility that a smoker is a male.

: Hello, Brett!
: Boy, this is really hard...

: Suppose there 100 people (try it when percents are involved).
: Then there are 40 males and 60 females.

: 50% of the males smoke -- um, that's HALF of them... uh... 20 ?

: And "20 out of 100" is...? (Where's my calculator?)

: ~~~~~~~~~~

As usual, when it comes to probability, I am probably looking at the problem incorrectly...

but, using your example (100 people considered), then if there are 20 male smokers, you can reason that there are also 18 female smokers.

so out of 100, 38 people smoke. also, if we consider the question "what is the probability that a smoker is male?", I read this as "out of 38 people, what is the probability that one of them is a male", or in other symbols, 20 out of 38 are male (from this group),

...so I see the probability of a smoker being male as 10/19 (or appx. 0.53).

I just see this as a probability of an event given "an event". [i.e. P(E|A)=P(smoker is male|smoker)]

just my interpretation... (as stated above, probability is not my field)

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