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:

If a and b are different positive integers and a + b = a(a + b), then which of the following must be true? I. a = 1 II. b = 1 III. a < b

A. I only B. II only C. III only D. I and II E. I and III

This is slightly tricky. Watch out! Don't get angry if your answer didn't match the OA. I want to have a discussion around this. ---- Kudos if you like this!

\(a + b = a(a + b)\) --> \(a(a+b)-(a+b)=0\) --> \((a+b)(a-1)=0\) --> as \(a\) and \(b\) are positive the \(a+b\neq{0}\), so \(a-1=0\) --> \(a=1\). Also as \(a\) and \(b\) are different positive integers then \(b\) must be more than \(a=1\) --> \(a<b\) (\(b\) can not be equal to \(a\) as they are different and \(b\) can not be less than \(a\) as \(b\) is positive integerand thus can not be less than 1).

So we have that: \(a=1\) and \(a<b\).

I. a = 1 --> true; II. b = 1 --> not true; III. a < b --> true.

Awesome! This was the exact point I wanted to bring up. And I was hoping for Bunuel to reply to the post. Thanks dude.

A and B are distinct positive integers. Why can't B be 0? Isn't 0 a positive integer? It sure as hell isn't negative. And indeed WIKI says "An integer is positive if it is greater than zero and negative if it is less than zero. Zero is defined as neither negative nor positive."

So per GMAT ..is zero positive or neither positive or negative?

Awesome! This was the exact point I wanted to bring up. And I was hoping for Bunuel to reply to the post. Thanks dude.

A and B are distinct positive integers. Why can't B be 0? Isn't 0 a positive integer? It sure as hell isn't negative. And indeed WIKI says "An integer is positive if it is greater than zero and negative if it is less than zero. Zero is defined as neither negative nor positive."

So per GMAT ..is zero positive or neither positive or negative?

Thank you again ..Bunuel.

Zero is neither positive not negative integer. _________________

a+b = a(a+b). to make the statement true a=1,b=2 1+2=1(1+2) 3 =3.

from this we know ,a=1 & a<b. answer should be E

Number picking might not be the best way to solve MUST BE TRUE questions.

The question asks which of the following MUST be true, or which of the following is ALWAYS true no matter what set of numbers you choose. For such kind of questions if you can prove that a statement is NOT true for one particular set of numbers, it will mean that this statement is not always true and hence not a correct answer.

So the set you chose just proves that II is not always true and hence it's not a part of a correct choice. As for I and III: they might be true for this particular set of numbers but not true for another set, so you can not say that I and III are always true just based on one set of numbers (it just happens to be that I and III are always true).

As for "COULD BE TRUE" questions: The questions asking which of the following COULD be true are different: if you can prove that a statement is true for one particular set of numbers, it will mean that this statement could be true and hence is a correct answer.

Tricky one indeed. I marked E but was wrong in solutioning. I thought a=-b means a is smaller than b. Didn't realise that this equation is not possible since both a and b are positive _________________

If you like my post, consider giving me some KUDOS !!!!! Like you I need them

a+b=a(a+b) 1(a+b)-a(a+b)=0 (1-a)*(a+b)=0 from this either a-1=0 or a+b=0, but since a and b are positive their could not be equal to 0. Thus, 1-a=0 or a=1. 1. holds true 2.not true because a and b are different positive integers and we know that a=1 3. true- As a, b are "different positive integers" when 1 is the smallest , thus a<b.

If a and b are different positive integers and a + b = a(a + b), [#permalink]

Show Tags

12 Dec 2012, 19:32

\(a+b = a (a+b)\) \(\frac{a+b}{a+b}=a\) \(a=1\)

I. a = 1 always TRUE II. b = 1 b must not be the same as a. Thus, b is not equal to 1. FALSE III. a < b b is a positive integer but not equal to 1 then it must be 2 onwards. always TRUE

Re: If a and b are different positive integers and a+b=a(a+b) [#permalink]

Show Tags

11 Feb 2015, 08:38

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________

Re: If a and b are different positive integers and a+b=a(a+b) [#permalink]

Show Tags

12 Mar 2016, 19:38

hemanthp wrote:

If a and b are different positive integers and a + b = a(a + b), then which of the following must be true?

I. a = 1 II. b = 1 III. a < b

A. I only B. II only C. III only D. I and II E. I and III

we can rewrite the equation as: (a+b)/a = a+b a/a=1 a+b/a = a+b we can subtract a from both sides b/a=b this is true only when A is 1. since we are told that the numbers are different, and both positive, we know for sure that b MUST be >1, or b>a.

E

gmatclubot

Re: If a and b are different positive integers and a+b=a(a+b)
[#permalink]
12 Mar 2016, 19:38

Part 2 of the GMAT: How I tackled the GMAT and improved a disappointing score Apologies for the month gap. I went on vacation and had to finish up a...

Cal Newport is a computer science professor at GeorgeTown University, author, blogger and is obsessed with productivity. He writes on this topic in his popular Study Hacks blog. I was...

So the last couple of weeks have seen a flurry of discussion in our MBA class Whatsapp group around Brexit, the referendum and currency exchange. Most of us believed...