PS Number properties

Hi sud21,

This question can be solved with Number Properties or by TESTing VALUES. Here's how you can answer it quickly by TESTing VALUES.

We're told that M and N are both POSITIVE INTEGERS and the UNITS DIGIT of their produce is 3. We're asked which of the following are factors of N.

Since the units digit is 3, the simplest pair of values would be....

M = 1
N = 3

(or vice-verse)

None of the numbers (8, 15 or 30) are factors of 3, so the correct answer should stand out...

Final Answer: E

GMAT assassins aren't born, they're made,
Rich

sud21 wrote:When positive integer m is multiplied by positive integer n , the units digit of the product is 3. Which of the following are factors of n ?
I. 8
II. 15
III. 30

A) I only
B) II only
C) I and II only
D) II and III only
E) None of the above

It's important to know that the question reads Which of the following ARE factors of n?
It doesn't say, Which of the following COULD BE factors of n?
This means we can quickly eliminate some statements be PLUGGING in numbers.

Rich used m = 1 and n = 3.
We could also use m = 3 and n = 11, or any variety of options.

Since none of the options (8, 15, 30) are factors of 11, the correct answer is E