If ab+c is odd?

[mosstashar1]

Hi,

In the number properties guide, third edition pages # 31.

The question ab+c is odd which of the following must be true? ...etc..

The answer seems too long to do! is there any easier way to do that becasue the schedule itself will take at least 2 minute or longer for me ..


Thanks
Mosst

[StaceyKoprince]

The questions in the guide are not in the form of GMAT questions. They are math questions designed to test whether you understand the theory of the math itself. You wouldn't have to do that kind of work on the real test. What you should learn, though, is the general principles. It's always going to be the case, for example, that even + odd = odd, so one of the two quantities (ab) and (c) has to be even and one has to be odd. And so on. Memorize the "must be true" principles and then you won't have to do all of the work on the test. You'll just know. (And it will be easier to remember if you actually understand WHY the principles are true, which is why we ask you to go through the work of figuring it out.)