Divisibility questions - quickest way to solve?

smehmood

We see lot of divisibility type of questions in GMAT as shown in the attached. What is the quickest way to solve these type of questions.
I would solve the attached by plugging different values for k and then see if it is divisible. Not sure if this is the quickest way to solve these type of questions.
Please advise.
Thanks
M

Vignesh.4384 · Posted: Fri Aug 15, 2008 7:07 pm Post subject:

Factorize .. You wil see the answer quickly

smehmood · Posted: Sat Aug 16, 2008 3:48 am Post subject:

Thanks for the reply.
Sorry I didn't understand. Factorize what?
Could you please explain?
M

sumithshah · Posted: Sat Aug 16, 2008 11:23 am Post subject:

Here are my two cents

We need to prove is k has at least powers of 2.

a) 8K is divisible by 16, that means K must have one power of 2. We need 2 powers of 2 - so since we aren't sure if k has one or more powers of 2, we can say it is insufficient

b) 9K is divisible by 12 means 3*3*K is divisible by 12, which would imply that K has atleast 2 powers of 2 ( which is basically what we need). Therefore sufficient.