I have written down some number properties. Just wondering if they're helpful in any way for the gmat.
1. For an odd number of consecutive numbers in a set, the sum is always a multiple of the number of items.
2. For an even number of consecutive numbers in a set, the sum is never a multiple of the number of items.
3. If you add or subtract multiples of an integer, you get another multiple of that integer.
4. Add a multiple of N to a non-multiple, result is non-multiple.
5. Add 2 non multiples of N and the result could be either multiple or non-multiple.
Just wondering if you guys have ever used any of these properties during your GMAT or practice exams. Thanks.
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are any of these facts helpful in any way?
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Ian Stewart
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I've never seen a real GMAT question where items 1 or 2 above might be at all helpful. I have seen one or two test prep company questions where you can use those facts, but it's not the type of thing you'd be expected to know on the real test.
Item 3 is absolutely fundamental in Number Theory. It's an extremely useful fact to understand, and is tested in various ways all the time, at all levels of the test. Item 4 is essentially a corollary of 3, and is also frequently tested (the infamous 'h(n)' question from GMATPrep is just one example). Item 5 doesn't really say anything, but you'd certainly want to know that, when you add two non-multiples of 8, for example, that you can sometimes get a multiple of 8 (5 + 3 = 8).
Item 3 is absolutely fundamental in Number Theory. It's an extremely useful fact to understand, and is tested in various ways all the time, at all levels of the test. Item 4 is essentially a corollary of 3, and is also frequently tested (the infamous 'h(n)' question from GMATPrep is just one example). Item 5 doesn't really say anything, but you'd certainly want to know that, when you add two non-multiples of 8, for example, that you can sometimes get a multiple of 8 (5 + 3 = 8).
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