GMATPrep - Another trap

givemeanid · Posted: Mon Sep 03, 2007 9:09 am Post subject: GMATPrep - Another trap

I came across this while taking a GMATPrep test.

If k is a positive integer, then 20k is divisible by how many different positive integers?

1. k is prime
2. k = 7

agps · Posted: Mon Sep 03, 2007 9:22 am Post subject:

I would answer D (either)

2) (easier) 20k = 20*7 = you know the number then you can determine all possible factors, sufficient.

1) any prime is divisible only by itself and 1. any prime multiplied by 20 will be divisible by it's factors and the factors of 20 (2, 4, 5, 10) so it's sufficient.

OA?

givemeanid · Posted: Mon Sep 03, 2007 9:37 am Post subject:

That's why its a trap son Smile

Try it again. D is not the OA

agps · Posted: Mon Sep 03, 2007 9:48 am Post subject:

hmmm,
is it because of 2? 2 is a prime, but also a factor of 20, then, not knowing what prime nuber it is you can't be sure if you have 4 different factors (for 2) or 5 (for any other prime number)

it that case, the answer would be B.

givemeanid · Posted: Mon Sep 03, 2007 12:47 pm Post subject:

Now you got it. You have to consider 2 (or 5) as a value of k!