Conditional probability tree diagram example | Probability | AP Statistics | Khan Academy

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Using a tree diagram to work out a conditional probability question. If someone fails a drug test, what is the probability that they actually are taking drugs?
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[@aaronastolfi7478]

Sal got me through my engineering degree, thank you!

[@bivshiyzek]

Fascinating! Thanks, Sal, I'm your biggest fun. I skipped a lot at school, and you're helping me to fill in the gaps. Greetings from Brazil.

[@sasi849]

I love this the best probability video I've ever played. Thanks

[@udaygawande104]

True

[@MrNecropolice]

Nice explanation. Thank you.

[@asdfire]

Great hitmarker cursor

[@bobthebb-illder827]

lmaoooo 😂💀

[@Josh-xo8wd]

@@bobthebb-illder827 Makes me wonder if he plays CS:GO

[@ethanmartinez836]

The way he explains math better than anyone else

[@Josama0214]

This isn't math?

[@mathteacher2651]

Well done!
thank you

[@Sukant98]

Really helpful thanks

[@aqsavidhra7488]

thank you sal

[@udaygawande104]

Good explanation

[@billyboi1662]

Thank you

[@dawitdereje2690]

You are the best

[@yassinovo]

if it is stated that 5% of the applicants are actually on drugs, shouldn't the test be irrelevant when selecting randomly?

[@obeytheMIGHTY]

shouldnt you multiply the 500 on drugs by the true positive rate not the true negative rate

[@Jim99O]

Did he mix up false negative and positives, or am I just confused?

[@edmondmwelwa5826]

U are right

[@rafansyed8420]

Sal tryna explain that he didn't do drugs
You're not fooling anyone

[@marianedaguno9709]

Is this a dependent or independent pls someone tell me

[@BillySmith-p4d]

Dependent.
First event is whether applicant on drugs or not. Second event is whether test positive or negative. Second event's probability depends on outcome of first event, so events are dependent.
Hopefully this is useful after 7 months )

[@elnurmmmdov436]

why didn't we divide by 500+190?

[@richidubey8301]

Because we arent checking for the case where the test shows +ve.

[@3a9im27]

Better call Sal:-)

[@GraceTerpstra]

R U TAKING DRUGS?

[@12345Hossam]

But aren't the 2% actually on drugs also since they tested positive? Since the 2% is a false positive rate, they got the result of not being on drugs incorrectly. So given the applicant tests positive, the probability they are actually on drugs are 100%. (I'm overthinking this maybe..)

[@sd-xk7qr]

2% false positive rate means that the test shows someone who is NOT on drugs is on drugs 2% of the time

[@anthonyjake15]

first :)

[@jackleaves4948]

Jake Ramirez 🅱️

[@sirjoshuafaw]

bro this is wrong.