Hi gmatmania17,
nkdotgupta is describing the Tic-Tac-Toe Board approach to Overlapping Sets questions; I'm a big fan of this approach since it helps solve both standard and "quirky" versions of this type of prompt. Since this question asks us to deal with the standard terms in an Overlapping Sets question, you COULD use the following formula to answer it:
Total = Group A + Group B - Both + Neither
Group A = Foreign stamps
Group B = More than 10 years old
Both = BOTH Foreign and More than 10 years old
Neither = NEITHER Foreign NOR More than 10 years old
200 = 70 + 50 - 20 + Neither
200 = 100 + Neither
100 = Neither
So, the number of stamps that are NEITHER Foreign NOR More than 10 years old is 100
Final Answer:
GMAT assassins aren't born, they're made,
Rich
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