If a is divided by 7 OR by 18, an integer results. Is a/42 an integer?
(to be answered with Yes, No or Cannot be determined)

My original answer was Yes because I overlooked "OR" and my understanding was "AND"; hence, I changed my answer to "Cannot be determined". However, when I checked the answer, the answer is based on "AND" instead or OR in the problem; hence it's "Yes".

It's more than just a typo error here. :)

I do agree that the answer is "Yes" if a is divisible by 7 AND 18. What if a is divisible by 7 OR 18? Would the answer alter? (Just confirming my understanding of the concept.)

Thanks in advance!

now the OR part means that a has been divided by 18 (besides 7) to give an integer, so in terms of solving it actually means

a is divisible by both 7 and 18.

Good question. When we say "if a is divided by 7 or 18, an integer results" we mean that a can be divided by either one, aka it is divisible by either one. It would be different if we said: "a can be divided by one or the other of 7 and 18, but not both."

Hi All,

I just started with my GMAT preparation and came across the 1st question in Number Properties (Guide One) on page 21.

The question says "If a is divided by 7 or by 18, an integer results. Is a/42 an integer?"

I solved this question and realized that the answer will be NO. Because the number is divided by 7 or by 18. So lets take an example, say, 70 which is divisible by 7 and results in an integer however 70/42 doesn't. Same goes with 80 which is divisible by 8 and yields an integer but 80/42 doesn't.

However, when I referred to the solution set on page 23 the explanation changes and it says "If a is divisible by 7 and by 18....". These two words change the question completely. And then the explanation on page 23 is certainly justified and the answer YES makes sense.

I read the explanation above but somehow I am not convinced. Anyways.. thought to open the thread again just to make sure that there are any alternate thoughts to it. Otherwise I will align my thoughts to the one posted by the MGMAT Staff :)

The switch between "or" and "and" changes nothing, because other words are changed as well and the two sentences mean exactly the same thing:

If a is divided by 7 or by 18, an integer results.
a is divisible by 7 and by 18.

These mean the same thing, namely that it doesn't matter whether you divide by 7 or 18 because both 7 and 18 will give you an integer..

The biggest thing i need to caution you about here is NEVER to decide that you have a definite NO just because you've tested one number (the same goes for a definite YES). You also need to be very careful to read the questions correctly; 80 being divisible by 8 has nothing to do with this problem, and it looks like you turned 18 into 8 when you started working on the problem..

_________________
Tim Sanders
Manhattan GMAT Instructor