Three drugs: A, B and C 50 subjects reported relief from: 21 drug a 21 drug b 31 drug c 9 a&b 14 a&c 15 b&c 41 report relief from at least one drug Note that some of the subjects who reported results from A might have done so for B and C etc. a. How many got relief from none of the drugs? I assume I use the difference rule here 50 - 41 = 9 subjects that didn't report any relief. b. How many people got relief from all 3 drugs? D[A intersection B intersection C] = 21 + 21 + 31 - 9 - 14 - 15 = 35 such that 41 - 35 = 6 The number of subjects relieved by all three drugs. c. How many subjects got relief from A only? I'm kind of unsure about this question. D[A - (A intersection B) - (A intersection C)] So how do I identify the specific users that have ticked in both a int b and a int c? 21 - 9 - 14 + 6 = 4 This is all I can think off.