help with this biostat question - usmle870

[ArchivalUser]

please help how to solve this ques with explanation

a test has 90 % sensitivity and 80 % specificity . 10 out of 100 have colorectal cancer. what is the positive predictive value of test?

[ArchivalUser]

Make the table

-----------------disease present---------disease absent
test +--------------9--------------------------8-----
test- ---------------1--------------------------72---------
total-----------------10-----------------------90------------



now PPV is 9/17

is that the answer?

[ArchivalUser]

ok i got the explanation from somewhere


-----------------------disease present---------------------disease absent

test + ------------------9-------------------------------------18 NOT 8

rest everything is fine.
answer is 9/27