Hi GMATbuster92,
On the GMAT, a "set" of numbers is a 'group' of numbers. Unless the prompt gives you information that 'restricts' what could be in the set, then ANY number is possible - including duplicate numbers. The specific wording of the prompt dictates how you should think about the information provided. For example, consider...
Set X = {1, 3, 5, Z}
We're not told ANYTHING about Z, so that variable could be ANY value. It's not necessarily greater than 5 and it's not necessarily an odd number - again, because we have not been told anything about Z. By extension, Z could potentially be 1, 3 or 5.
If a question asks you to combine two sets and asks for the number of 'different' elements, then THAT would mean we should ignore the duplicates...
Set A = {1, 2, 3} and Set B = {2, 3, 4}
Combining these sets, the number of DIFFERENT elements would be 4 --> {1, 2, 3 and 4}
A similar concept can sometimes appear in Prime Factorization questions...
How many DISTINCT Prime factors are there in the number 24?
24 = (2)(2)(2)(3).... so while there are technically 4 prime numbers (three 2s and one 3), there are only 2 DISTINCT prime factors (2 and 3).
This is all meant to say that you have to pay attention to whatever 'restrictions' the prompt places on you (including the specific question that the prompts asks you to solve).
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Rich
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