divisibiity

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resilient: Legendary Member; Posts: 789; Joined: Sun May 06, 2007 1:25 amFollowed by: 6 members; Location: Southern California, USA; Thanked: 15 times

by resilient » Fri May 09, 2008 6:06 pm

1. Which of the following numbers CANNOT be divisible by 6?
(A) 2,210,208
(B) 2,596,536
(C) 4,529,910
(D) 4,262,216
(E) 1,859,916

qa is d

Appetite for 700 and I scraped my plate!

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Source: Beat The GMAT — Problem Solving | Fri May 09, 2008 6:06 pm

VP_Jim: GMAT Instructor; Posts: 1223; Joined: Thu May 01, 2008 3:29 pmFollowed by: 15 members; Location: Los Angeles, CA; Thanked: 185 times

by VP_Jim » Fri May 09, 2008 7:27 pm

Hi resilient,

An easy way to look at this problem is to recall that any number divisible by 2 and 3 is also divisible by 6. All the numbers are divisible by 2 because they're even. So, now we just need to check which answer is NOT divisible by 3. To check if a number is divisible by 3, add up the digits in each of the answers. If the digits add up to a number that is divisible by 3, the whole number is divisible by 3. Thus, you find out that only D is NOT divisible by 3 because its digits add up to 23.

Hope this helps!

Jim S. | GMAT Instructor | Veritas Prep

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Luca80: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Mon Apr 14, 2008 6:26 am; Thanked: 2 times

by Luca80 » Sat May 10, 2008 12:18 am

good explanation VP_jim

remember that summing the digits of the number you do not need to know the total value, but only if it is divisible by 3.

so for example

2,596,536

do not sum all the digits. you already know that 9 6 12 are divisible by 3. thus look only at other and sum them

ciao

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resilient: Legendary Member; Posts: 789; Joined: Sun May 06, 2007 1:25 amFollowed by: 6 members; Location: Southern California, USA; Thanked: 15 times

divisibiity

by resilient » Sat May 10, 2008 6:15 am

Wow, thanks for the great answer. I am was having some problems with divisiibility. BUt I am learning that adding the numbers and seeing if divisibile will possible is the key take away. Excellent explanation!

IS it possible for you to give one more questions to further explain?

Appetite for 700 and I scraped my plate!

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