Can anyone help with this problem. Trying to help my bro with his statistics homework, but I really don't remember shit about probability trees.

Using a probability tree:
If a certain disease is present, the a blood test will reveal it 95% of the time. but the test will also indicate the presence of the disease 2% of the time when in fact the person is free of the disease( false positive). If it is known that 0.3% of the Population actually has the disease, what is the probability that a person chosen at random from the population has the disease given that he/she tested positive.

You draw the first branch for the probability of a person actually having/not having the disease.
Then from there, another branch from each of those the blood test probabilities.

so your first 2 branches will be 0.3% for yes, and 99.7% for no.
then branching off of the 0.3%(yes branch) will be: 95% for yes, 5% for no
branching off of the 99.7%(no branch) will be: 2% for yes, 98% for no.

Now for calculating your probabilities, just follow each branch until the end for your desired answer!

ah man was it really that simple? lol

Thanks a lot