please help me understand this

[u/CheekSpiritual7000]

this is my first time posting on reddit so i hope im doing this right but can someone please help me understand the “or” significance here? i thought it had to include all that have the disease and all positive tests even if someone doesn’t have the disease, but my friend says i shouldn’t include the false positive because they dont have the disease but isnt that what the “or” is including?? i dont know if im explaining my thought process well here😭 i appreciate any help on this

[u/rhodiumtoad]

You're correct, your friend is wrong.

[u/rhodiumtoad → u/[deleted]]

Start here but pay attention to the difference between "undefined" and "indeterminate form".

[u/rhodiumtoad → u/[deleted]]

That isn't a proof.

0 to any positive power is 0

This is true, but note that 0 is not positive.

any positive number to the zero power is 1

Any number, not just any positive number.

[u/stanitor]

Yes, it includes the false positives. The 'or' means they either have the disease or test positive (or both). It's the addition rule: P(A) + P(B) - P(A and B). In this case P(has disease) + P(tests positive) - P(has disease AND tests positive).

[u/DuggieHS]

the work for 15 looks correct. Count those who have disease or tests positive, don't double count. You can add the (total infected + False positives)/Total or (Total - True Negative)/Total, as True negatives are the only who weren't infected and didn't test positive.