How does b) factor those who failed both written and physical?
It doesnt need to. The question asks for how many passed both.
4/5 of applicants passed the physical examination-
given 100 applicants, 80 passed, 20 did not
3/4 of those who passed the physical passed the written-
80 passed physical, 3/4 of whom passed written-
60 passed both, the answer to what the stem asked.
"Any school that meets you and still lets you in is not a good enough school to go to" - my mom upon hearing i got in