View Full Version : How do I add percentages?

cpaavola

04-30-2010, 12:30 PM

For instance, let's say a person is a truck driver and there's an:

80% chance of they smoke

40% chance of they are overweight

60% chance of they are male

If we grab one person at random who is a truck driver, what's the chance they smoke, are overweight AND are male? Or, what's the chance they smoke and are male but are not overweight?

Thanks!

vinux

04-30-2010, 01:41 PM

Hint:

If you are assuming the qualities are indepenent .. Use the property of probability of independent events.

P(A and B)= p(A)*P(B).

cpaavola

04-30-2010, 02:05 PM

So, the probability of al three occuring is:

(80 X 40 X 60) / (100 X 100 X 100) = 19.2%

Is that correct? Sorry, I'm not a stats guy, but I like those who are!

statsguy

05-03-2010, 12:18 AM

So, the probability of al three occuring is:

(80 X 40 X 60) / (100 X 100 X 100) = 19.2%

P(A and B and C) = (.80)(.40)(.60)

P(A and not B and C) = (.80)(1-.40)(.60) = (.80)(.60)(.60)

For independent events A and B, the probability of their intersection is the product of the individuals probabilities. Don't sum probabilities in this case; that only applies for events that are disjoint (which they are not here, clearly.)

Is that correct? Sorry, I'm not a stats guy (I'm statsguy), but I like those who are!

Hope this helps!

cpaavola

05-03-2010, 12:15 PM

Hope this helps!

Hahaha... your name suits you! Thanks man. :wave:

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