Hey Leo! I'm assuming that you're talking about the SCJP. Yes, I would assume that you would never want to use a floating-point number for an equality test. However, I've never heard anyone say that you need to know this type of stuff for the test. Also, a better forum for this question would be the Programmer Certification Study forum. It's the best test forum that I've used.
Can we assume that all floating point arithmetic will produce a false equality test? No, definitely not. You can assume that any floating-point equality test may give a false result even though true is expected - but it also may give true. You're not expected to be able to predict the result in a case like the one you showed. You should know that a -b/c is approximately 1/3, and a/c is also approximately 1/3 , and that these two approximations may or may not be equal to each other.
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