I've found these problems particularly tricky as it is easy to misread or not test 1 type of case...
It is true that tough statistic and set problems are tricky where chances of misreading are max becoz the problems are lengthy always..
My personal approach for these problems to avoid the misreading is to break the problem into pieces then and there, and jotting down the data in a simple tabular or diagram form (which ever is suitable).
It may be little time consuming, yet it avoids definite misreading or interpreting errors..
And finally the more you practice these type, the faster and easier will be your answer (since these types of problems basically have fixed number of variation).
Hemanth.
