Divisibility questions - quickest way to solve? - The Beat The GMAT Forum

Divisibility questions - quickest way to solve?

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smehmood: Senior | Next Rank: 100 Posts; Posts: 54; Joined: Sat May 10, 2008 1:48 pm

by smehmood » Fri Aug 15, 2008 5:33 pm

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

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Source: Beat The GMAT — Data Sufficiency | Fri Aug 15, 2008 5:33 pm

Vignesh.4384: Master | Next Rank: 500 Posts; Posts: 443; Joined: Sat Jun 28, 2008 6:33 pm; Thanked: 5 times

by Vignesh.4384 » Fri Aug 15, 2008 7:07 pm

Factorize .. You wil see the answer quickly

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smehmood: Senior | Next Rank: 100 Posts; Posts: 54; Joined: Sat May 10, 2008 1:48 pm

by smehmood » Sat Aug 16, 2008 3:48 am

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

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sumithshah: Master | Next Rank: 500 Posts; Posts: 165; Joined: Wed May 28, 2008 11:25 pm; Thanked: 9 times; GMAT Score:730

by sumithshah » Sat Aug 16, 2008 11:23 am

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.

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