is it C 8??
how many patients will have the diagnosis of disease X missed by this test?
simply they r asking about False negative....they hv given 5% prevalence rate...so out of 1000.... 50 will hv disease...means in 2*2 table we hv TP+FN=50
TP=85% * (TP+FN)
we hv TP+FN=50....so FN is 50-TP=8