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 350,000 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:

Re: Math: Number Theory [#permalink]
05 Mar 2010, 13:06

Bunuel wrote:

The topic is done. At last!

I'll break it into several smaller ones in a day or two.

Any comments, advises and/or corrections are highly appreciated.

What Topic are we talking abt?? _________________

Cheers! JT........... If u like my post..... payback in Kudos!!

|Do not post questions with OA|Please underline your SC questions while posting|Try posting the explanation along with your answer choice| |For CR refer Powerscore CR Bible|For SC refer Manhattan SC Guide|

Re: Math: Number Theory [#permalink]
17 Mar 2010, 13:43

Hi Bunnel,

I m confused about the extent of level for number properties.. do we have to remmeber eculer's, fermat's,wilson's theorem on prime number. Actually I found their application to be quite useful but m not sure whther there are other ways to solve the questions as well. eg difficult remainder questions and questions on HCF like if HCF of 2 numbers is 13 and their sum is 2080, how many such pairs are possible? do we see such questions on gmat? _________________

Re: Math: Number Theory [#permalink]
17 Mar 2010, 14:07

Expert's post

gurpreetsingh wrote:

Hi Bunnel,

I m confused about the extent of level for number properties.. do we have to remmeber eculer's, fermat's,wilson's theorem on prime number. Actually I found their application to be quite useful but m not sure whther there are other ways to solve the questions as well. eg difficult remainder questions and questions on HCF like if HCF of 2 numbers is 13 and their sum is 2080, how many such pairs are possible? do we see such questions on gmat?

I don't think that these theorems are needed for GMAT. _________________

Re: Math: Number Theory [#permalink]
17 Mar 2010, 14:29

So is there any way we can solve the above HCF question? Also does the number theory stated here is sufficient to cover the concepts asked? _________________

Re: Math: Number Theory [#permalink]
30 Apr 2010, 13:30

Expert's post

AloneAndInsufficient wrote:

Bunuel wrote:

NUMBER THEORY • For GMAT it's good to memorize following values: \sqrt{2}\approx{1.41} \sqrt{3}\approx{1.73} \sqrt{5}\approx{2.24} \sqrt{7}\approx{2.45} \sqrt{8}\approx{2.65} \sqrt{10}\approx{2.83}

Anyone else notice that these are wrong? They should be: • For GMAT it's good to memorize following values: \sqrt{2}\approx{1.41} \sqrt{3}\approx{1.73} \sqrt{5}\approx{2.24} \sqrt{6}\approx{2.45} \sqrt{7}\approx{2.65} \sqrt{8}\approx{2.83} \sqrt{10}\approx{3.16}

Thanks. Edited. +1 for spotting this. _________________

Re: Math: Number Theory [#permalink]
10 May 2010, 15:51

Expert's post

sag wrote:

Example: A company received $2 million in royalties on the first $10 million in sales and then $8 million in royalties on the next $100 million in sales. By what percent did the ratio of royalties to sales decrease from the first $10 million in sales to the next $100 million in sales?

Solution: Percent decrease can be calculated by the formula above: Percent=\frac{Change}{Original}*100=\frac{\frac{2}{10}-\frac{10}{100}}{\frac{2}{10}}*100=50%, so the royalties decreased by 50%.

I could not get this , i think there is some error... Plzz explain..

as the same Q in Percent Part of Math book is giving an answer of 60 %..

There was a typo. I edited it in Percent section and forgot to edit it here. Now it's OK. Thanks. +1 for spotting this. _________________

Re: Math: Number Theory [#permalink]
12 May 2010, 12:53

sag wrote:

Example: A company received $2 million in royalties on the first $10 million in sales and then $8 million in royalties on the next $100 million in sales. By what percent did the ratio of royalties to sales decrease from the first $10 million in sales to the next $100 million in sales?

Solution: Percent decrease can be calculated by the formula above: Percent=\frac{Change}{Original}*100=\frac{\frac{2}{10}-\frac{10}{100}}{\frac{2}{10}}*100=50%, so the royalties decreased by 50%.

I could not get this , i think there is some error... Plzz explain..

as the same Q in Percent Part of Math book is giving an answer of 60 %..

2 million royalties on 10 million in sales is equivalent to 20 million royalties on 100 million sales (multiply both number by 10). Going down from 20 million royalties to 8 million royalties is a decrease of 60%.

Re: Math: Number Theory [#permalink]
10 Jun 2010, 14:00

Expert's post

bely202 wrote:

If a is a factor of bc, and gcd(a,b)=1, then a is a factor of c.

Can anyone please explain this rule??? I'm not sure what it means by gcd(a,b)=1.

Thanks a bunch and great summary !!!!!

gcd(a,b)=1 means that greatest common divisor of a and b is 1, or in other words they are co-prime, the don't share any common factor but 1. So if we are told that a is a factor of bc and a and b don't share any common factors, then it must be true that a is a factor of only c.

So if a=3, b=5 (a and b don't share any common factors but 1, gcd(a,b)=1), c=6bc=30 --> a=3 is a factor of c=6. _________________

My three goals of business school: entrepreneurship, network, and professor mentor. I want to build something. I want to meet new people and create life-long friendships. I want to...