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Schools: Tuck '16 (D) McCombs '16 (WL)
Posts: 25
Hey Bunuel,
In your Math Guide for a number divisible by 7 you give this trick:
Take the last digit, double it, and subtract it from the rest of the number, if the answer is divisible by 7
(including 0), then the number is divisible by 7.
Can you give me an example on how to use it? I tried with 21 but got stuck as I couldn't interpret it properly.
I took 21 as an example and did 1 X 2 to get 2. So now do i subtract 2 from 21 or 20? or just 2? In short when you say "from rest of the number" what does that mean?
Thanks for your wonderful guide and work on this forum
In your Math Guide for a number divisible by 7 you give this trick:
Take the last digit, double it, and subtract it from the rest of the number, if the answer is divisible by 7
(including 0), then the number is divisible by 7.
Can you give me an example on how to use it? I tried with 21 but got stuck as I couldn't interpret it properly.
I took 21 as an example and did 1 X 2 to get 2. So now do i subtract 2 from 21 or 20? or just 2? In short when you say "from rest of the number" what does that mean?
Thanks for your wonderful guide and work on this forum
Archived Topic
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Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
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patelsid
Take the last digit, double it, and subtract it from the rest of the number, if the answer is divisible by 7 (including 0), then the number is divisible by 7.
For example, let's check whether 1519 is divisible by 7: 151-2*9=133. Since 133 is divisible by 7 (133=7*19), then so is 1,519.
For 21: 2-2*1=0. Since 0 is divisible by 7, then so is 21.
Hope it's clear.
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@patelsid
The divisibility rule for the number 7 is of no use as far as the GMAT is concerned. It has never appeared in any form on the GMAT so far, and I don't anticipate seeing it on the exam. The divisibility rules for 2, 3, 4, 5, 6, 8, and 9 are definitely tested on the exam. (8 I haven't seen so far, but 4 I have).
Cheers,
Dabral
The divisibility rule for the number 7 is of no use as far as the GMAT is concerned. It has never appeared in any form on the GMAT so far, and I don't anticipate seeing it on the exam. The divisibility rules for 2, 3, 4, 5, 6, 8, and 9 are definitely tested on the exam. (8 I haven't seen so far, but 4 I have).
Cheers,
Dabral
Schools: Tuck '16 (D) McCombs '16 (WL)
Posts: 25
dabral
Thanks for that Dabrall, honestly it was something that was bothering me for a while since MGMAT guide also didn't have a divisibility rule for 7. So just wanted to know in general, but the fact that it is almost never tested on GMAT is great as well :D. Thanks
Schools: Tuck '16 (D) McCombs '16 (WL)
Posts: 25
Thanks Bunuel! That was a great example and now I can follow it easily. Once again, thanks for the time you take for the forum
Bunuel
Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
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