I have a few questions regarding multiples, factors and primes and I would really appreciate an input.

1. When a GMAT question asks you to find the total number of factors, should we include the negative factors as well? I have read the first book of your collection where it defines factors as positive numbers.. could someone elaborate on that a bit more please? The factors of 4 are 2 or 4? When the GMAT says factor should we assume that it means only positive ones, or we should not assume anything?

2. Also, when a GMAT question says that a number has 2 factors: Then someone could assume that it is a prime number. But if we define factors as negative numbers too, the only number with 2 factors would be 1. (Does it have to say only 2 factors to mean 2 numbers? or if it says 2 factors we could assume that there could be more?)

3. When a GMAT question says that a is divisible by b. Someone could say that a >= b. I would argue that -3 could be divisible by 1 therefore the aforementioned doesn't apply.

4. Also, when it talks about multiples of a number, should we include negative ones and 0 as well? Could we talk about multiples of a decimal number? or only of integers?

5. Can factors be decimal numbers? for example. 16 is divisible by 0,2 since the result is an integer. Can we say that 0,2 is a factor of 16?

6. If a questions says that n is divisible by 3. Can we say that n must be an integer because the product of 2 integers can only be an integer. Meaning, n=3*k, since k is integer, n must also be integer. Is the aforementioned logic correct?

7. If we know that a divides b. Can a and b be decimals? If they can be decimals, then b has infinite factors. for example if b is 0,3 then a could be 3/10, 3/20, 3/30 etc... Therefore a decimal has infinite number of factors? Could we assume that if it says that a number has a finite number of factors, that this number cannot be decimal? Therefore if it states that a number has only 2 positive factors, we can assume this is an integer (prime number) and not a decimal (since it has a finite number of factors?)

I would really appreciate an input.. and sorry for the huge post!

Not an answer yet :(.. If anyone has the same questions, they have been answered elsewhere..

http://gmatclub.com/forum/question-rega ... 22943.html

I take it you’ve gotten your questions answered then? Good work on doing the research yourself; I wish more students would.. :)

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Tim Sanders
Manhattan GMAT Instructor