Try this explanation: according to the condition, 'set it aside'. It means, that the sum of f_magazines and h_magazines is 2+4=6. Using this it is possible to re-write the finding the probability of the both events A&B: P(A)=3/7 - correct P(B|F)=4/7 - false! correct is P(B|A)=4/6=2/3 P(A&B)=3/7 * 4/7=12/49 - false! correct is P(A&B)=3/7 * 2/3=2/7≈0.2857
