OG - DS - #125

[Carla]

Question:

If r and s are positive integers, is r/s an integer?

(1) Every factor of s is also a factor of r.
(2) Everyprime factor of s is also a prime factor of r.

The correct answer is A.

When I went over this example I had chosen D which is incorrect. I am not clear on the difference between factors vs. prime factors - why would we only need (1) and not (2) above.

Thanks!

Carla

[GMAT 5/18]

Carla,

Statement II reads "Every prime factor of s is also a prime factor of r."

This means that S could have 2,2,3 as it's prime factors and R could have 2,3.

Statement II (Every prime factor of s (2 and 3) is also a prime factor of r (2 and 3).

6/12 = not an integer.

This is where it can get tricky - every factor means r/s will be an integer.

Hope that helps!

[Carla]

Hi,
That does help. Did you have a particular way to learn the Num. Prop problems.. I am finding them to be so tricky...
-Carla

[GMAT 5/18]

Everything I know about Number Properties, I learned from the MGMAT Number Property Strategies Guide. At the end of each chapter within the NPSG, there were 15 questions, of which the last 8 or so were very challenging. Every OG problem I have encountered thus far has been solvable using one of the methods listed in the NPSG.

My advice to you would be to invest in this book if you have not already done so. If you are currently using the book, I would live & breathe the rules and go the 15 questions at the end of each chapter.

Number Property questions are very tricky, but with practice, they are manageable.

Good luck!

[Carla]

I am working with that book too.. trying to every single example at the end of the chapters and every single example listed in the back of the book... hopefully this will work for me too!!...

[dbernst]

GMAT 5/18, great explanation! Also, as a disclaimer, GMAT 5/18 is neither employed by nor affiliated with Manhattan GMAT...he is simply smart enough to realize how superior our materials really are!!!

Thanks for the props.
-dan