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megafan
Joined: 28 May 2009
Last visit: 15 Oct 2017
Posts: 137
Given Kudos: 91
Location: United States
Concentration: Strategy, General Management
Schools: Stern PT Fall'18 Booth PT '18
GMAT Date: 03-22-2013
GPA: 3.57
WE:Information Technology (Consulting)
22 Jan 2013, 14:21
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I made a memory aid for FDPs a while ago, and it really helped me master FDP conversions. So, in a similar fashion, I made another one for Primes from 1-100 organized in 2 ways: 1. Tens digit 2. Units digit.
Hopefully you guys will find this helpful.
Hopefully you guys will find this helpful.
Attachment:
Primes 1-100.png
Attachment:
FDPList.png
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22 Jan 2013, 16:35
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The GMAT only expects one to know primes less than 100. If they are asking you to test for primes greater than 100, then it will be likely a different concept. For example, is 11! + 7 prime and why or why not?
But coming back to the primes less than 100, I prefer not to tax my brain by memorizing the numbers, instead only look for odd numbers(other than 2 which is prime) and see if they are divisible by 3, 5, and 7, if they are not divisible by 3, 5, and 7, then it is prime.
For example, 89 is not divisible by 3(digits add up to 17), is not divisible by 5(does not end in 0 or 5), and also not divisible by 7(you do have to actually do the division but it should be fairly quick). Therefore, 89 is prime.
Cheers,
Dabral
But coming back to the primes less than 100, I prefer not to tax my brain by memorizing the numbers, instead only look for odd numbers(other than 2 which is prime) and see if they are divisible by 3, 5, and 7, if they are not divisible by 3, 5, and 7, then it is prime.
For example, 89 is not divisible by 3(digits add up to 17), is not divisible by 5(does not end in 0 or 5), and also not divisible by 7(you do have to actually do the division but it should be fairly quick). Therefore, 89 is prime.
Cheers,
Dabral
megafan
Joined: 28 May 2009
Last visit: 15 Oct 2017
Posts: 137
Own Kudos:
Given Kudos: 91
Location: United States
Concentration: Strategy, General Management
Schools: Stern PT Fall'18 Booth PT '18
GMAT Date: 03-22-2013
GPA: 3.57
WE:Information Technology (Consulting)
22 Jan 2013, 16:42
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@dabral — I totally agree with you. In fact, that's the reason why I prefer these memory aids, which doesn't really tax my brain. I use Mind Maps and Memory palaces for other stuff too, and they improve my speed with little effort. I figured these aids might help those who are cognizant of the above mentioned Memory techniques—because they really are all about not taxing one's brain.
