Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

\(686\) Subtract twice the last digit (2*6) from the # formed by the remaining digits(68) \(68-12=56\) If the diff is divisible by 7, the original # is a multiple of 7. \(686-56=630\) 630 is divisible by 7 => 686 is divisible by 7.

I have never heard of this rule before. Hope I got it right (it should be right I tesed other numbers)
_________________

It is beyond a doubt that all our knowledge that begins with experience.

Lets break down the process in steps for easier understanding and throw couple of examples

1. Take the units digits or last digit in the number. Lets use 441 last digit is 1 and for 354 it is 4 ) 2. Double the last digits which will be 2 and 8 3. Subtract the number you doubled from rest of the digits which means ( 44-2 = 42 and 35 - 8 = 27) 4. Check if the result in Step 3 is divisible by 7. ( 42 divisbile by 7 - Yes (7 X 6 =42 then 441 divisible by 7. Similarly 27 not divisible by 7 so 354 is NOT divisible by 7) 5. Fist pump if you got the concept

\(686\) Subtract twice the last digit (2*6) from the # formed by the remaining digits(68) \(68-12=56\) If the diff is divisible by 7, the original # is a multiple of 7. \(686-56=630\) 630 is divisible by 7 => 686 is divisible by 7.

I have never heard of this rule before. Hope I got it right (it should be right I tesed other numbers)

This is the correct illustration of the "divisible by 7 shortcut". Nicely done.

Of course, it's hard to remember many obscure rules that will likely never become relevant on the GMAT, so take these rules with a grain of salt. The best strategy is still to logically and systematically drop multiples until you get to the right answer. For 686, you might be able to see that it's 14 away from 100, so this is 7x98. Otherwise drop multiples of 7, 70, 700, etc. 700 is too big, so we can drop 70x9=630, leaving us with 56 (or 7x8).

This technique is good because it works for all numbers quickly. The only ones you should definitely know are 2, 3, 5 and 10. All others may have simple shortcuts but being able to drop multiples quickly to determine divisibility is the most flexible strategy.

\(686\) Subtract twice the last digit (2*6) from the # formed by the remaining digits(68) \(68-12=56\) If the diff is divisible by 7, the original # is a multiple of 7. \(686-56=630\) 630 is divisible by 7 => 686 is divisible by 7.

I have never heard of this rule before. Hope I got it right (it should be right I tesed other numbers)

HulkSmashGMAT wrote:

Hi

Lets break down the process in steps for easier understanding and throw couple of examples

1. Take the units digits or last digit in the number. Lets use 441 last digit is 1 and for 354 it is 4 ) 2. Double the last digits which will be 2 and 8 3. Subtract the number you doubled from rest of the digits which means ( 44-2 = 42 and 35 - 8 = 27) 4. Check if the result in Step 3 is divisible by 7. ( 42 divisbile by 7 - Yes (7 X 6 =42 then 441 divisible by 7. Similarly 27 not divisible by 7 so 354 is NOT divisible by 7) 5. Fist pump if you got the concept

Cheers!

- Hulk

First of all thank you for the kind cooperation. In fact , I tried the rule with 63 and 56 it did not work , but it worked on trying it with 49 . This what making me puzzled
_________________

\(686\) Subtract twice the last digit (2*6) from the # formed by the remaining digits(68) \(68-12=56\) If the diff is divisible by 7, the original # is a multiple of 7. \(686-56=630\) 630 is divisible by 7 => 686 is divisible by 7.

I have never heard of this rule before. Hope I got it right (it should be right I tesed other numbers)

This is the correct illustration of the "divisible by 7 shortcut". Nicely done.

Of course, it's hard to remember many obscure rules that will likely never become relevant on the GMAT, so take these rules with a grain of salt. The best strategy is still to logically and systematically drop multiples until you get to the right answer. For 686, you might be able to see that it's 14 away from 100, so this is 7x98. Otherwise drop multiples of 7, 70, 700, etc. 700 is too big, so we can drop 70x9=630, leaving us with 56 (or 7x8).

This technique is good because it works for all numbers quickly. The only ones you should definitely know are 2, 3, 5 and 10. All others may have simple shortcuts but being able to drop multiples quickly to determine divisibility is the most flexible strategy.

Hope this helps! -Ron

Kudos for the great explanation .what about 56 , and 63 ? this rule did not work
_________________

Exactly. They still work if you consider negative numbers or 0. I guess the base case would be 7. We'd get 0 - (2x7) = -14, which is in fact divisible by 7.. but it would be a little silly to use this rule to check if 7 is divisible by 7

I'd say any 2 digit number should be pretty easy to do. The multiplication table takes you to 7x12 = 84. After that there's 91 and 98 and then triple digits. Feel free to use this for triple digits upwards, although again it's never the only way to check for divisibility.

It’s quickly approaching two years since I last wrote anything on this blog. A lot has happened since then. When I last posted, I had just gotten back from...

Since my last post, I’ve got the interview decisions for the other two business schools I applied to: Denied by Wharton and Invited to Interview with Stanford. It all...

Marketing is one of those functions, that if done successfully, requires a little bit of everything. In other words, it is highly cross-functional and requires a lot of different...