Dr. Grossman, an internist, has 520 patients, of which (i) 230 are hypertensive,

(ii) 185 are diabetic, (iii) 35 are hypochondriac and diabetic, (iv) 25 are all three, (v) 150 are none, (vi) 140 are only hypertensive, and finally, (vii) 15 are hypertensive and hypochondriac but not diabetic. Find the probability that Dr. Grossman’s next appointment is hypochondriac but neither diabetic nor hypertensive. Assume that appointments are all random. This implies that even hypochondriacs do not make more visits than others.