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: Number properties question [#permalink]
26 Jan 2010, 12:15

1

This post received KUDOS

roceeet wrote:

Which of the following could be the sum of the reciprocals of two different prime numbers?

(a) 7/13 (b) 10/21 (c)11/30 (d)23/50 (e)19/77

B..sum of reciprocals of 7 and 3.. _________________

--------------------------------------------------------------------------------------- If you think you can,you can If you think you can't,you are right.

Re: Number properties question [#permalink]
26 Jan 2010, 12:19

1

This post received KUDOS

roceeet wrote:

Which of the following could be the sum of the reciprocals of two different prime numbers?

(a) 7/13 (b) 10/21 (c)11/30 (d)23/50 (e)19/77

Two primes - a and b. [m]1/a + 1/b = (b+a)/(ab)[m]

So: (a) - not possible, because 13 is a prime - ab cannot equal 13. (b) - 7,3 work 7*3=31, 7+3=10, the answer is B...

(c) 30 -- 15,2 (not prime), 10,3 (not prime), 5,6 (not prime), 30,1 (not prime)... 30 does not factor into only two numbers (i.e. primes), so not possible. (d) Like 30, 50 will not factor into solely two primes. (e) 77 = 7 * 11, so two primes. 7+11 = 18, NOT 19, so not E. _________________

________________________________________________________________________ Andrew http://www.RenoRaters.com

Re: Number properties question [#permalink]
27 Jan 2010, 02:20

2

This post received KUDOS

Expert's post

If \(x<12\), then it must be true that:

(a) \(-x<-12\) --> \(x>12\) not true; (b) \(-x-2<14\) --> \(x>-16\) not always true; (c) \(-x+2<-10\) --> \(x>12\) not true; (d) \(x+2<10\) --> \(x<8\), not always true; (e) \(x-2<11\) --> \(x<13\) now if \(x<12\) (given), \(x\) will definitely be less than \(13\). Always true.

E.Add the 2 fractions and replace the value of xy. _________________

--------------------------------------------------------------------------------------- If you think you can,you can If you think you can't,you are right.

Re: Number properties question [#permalink]
28 Jan 2010, 15:20

a*b = a + b - ab given a*b = 0, then 0 = a + b -ab -b = a(1-b) b = a(b-1) a = b / (b-1) if b=1, then a becomes undefined. So b=1 cannot be valid. IMO B

Back to hometown after a short trip to New Delhi for my visa appointment. Whoever tells you that the toughest part gets over once you get an admit is...