Question 6585
Best thing to do with these questions is to draw a Venn diagram, which makes it easier to visualize the problem. I can't do that for you via the internet, but I'm sure you know what I mean because you're doing probability and Venn diagrams are a central part of probability. Basically you draw two circles that partially intersect each other within a rectangle. One of the circles is called Magazine A, and other Magazine B. Then you simply fill in the information you're given. Written mathetmatically, what they're asking you to find is P(AuB), which stands for the probability of AorB. The formula for this is P(AuB)=P(A)+P(B)-P(AnB). All you do now is plug in the values. Therefore:
P(AuB)=1200/2400+500/2400-100/2400=.5+5/24-1/24= 2/3 which is your answer.

Hope that helps.
Regards,
-Mike