• Economist Test Prep
    Free Trial & Practice Exam
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep
  • Kaplan Test Prep
    Free Practice Test & Review
    How would you score if you took the GMAT

    Available with Beat the GMAT members only code

    MORE DETAILS
    Kaplan Test Prep
  • PrepScholar GMAT
    5 Day FREE Trial
    Study Smarter, Not Harder

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep
  • Target Test Prep
    5-Day Free Trial
    5-day free, full-access trial TTP Quant

    Available with Beat the GMAT members only code

    MORE DETAILS
    Target Test Prep
  • Varsity Tutors
    Award-winning private GMAT tutoring
    Register now and save up to $200

    Available with Beat the GMAT members only code

    MORE DETAILS
    Varsity Tutors
  • e-gmat Exclusive Offer
    Get 300+ Practice Questions
    25 Video lessons and 6 Webinars for FREE

    Available with Beat the GMAT members only code

    MORE DETAILS
    e-gmat Exclusive Offer
  • The Princeton Review
    FREE GMAT Exam
    Know how you'd score today for $0

    Available with Beat the GMAT members only code

    MORE DETAILS
    The Princeton Review
  • EMPOWERgmat Slider
    1 Hour Free
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh

Operations with Rational Numbers

This topic has 5 expert replies and 0 member replies
jmacym Newbie | Next Rank: 10 Posts
Joined
29 Sep 2016
Posted:
6 messages

Operations with Rational Numbers

Post Sat Oct 08, 2016 10:42 am
One of my review questions...

The sum 7/8 + 1/9 is between...

The correct answer is (B) 3/4 and 1

The explanation is as follows: Since 1/9 < 1/8, 7/8 + 1/9 < 7/8 + 1/8 = 1 answer choices C, D, and E can be eliminated.
Since 7/8 > 6/8 = 3/4, 7/8 + 1/9 > 3/4 answer choice A can be eliminated. Thus, 3/4 < 7/8 + 1/9 < 1

Okay, so my thinking is first of all 7/8 + 1/9 is 71/72... obviously that was not even close to any of the answer choices.
The explanation confuses me even more because it's saying 1/9 is less than 1/8...which I understand how and why that is true, but 1/9 could be less than TONS of numbers. How am I supposed to know to use 1/8 instead of, lets say, 1/7 or 1/6, 1/5..etc. to get to the correct answer?

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

DavidG@VeritasPrep Legendary Member
Joined
14 Jan 2015
Posted:
2667 messages
Followed by:
120 members
Upvotes:
1153
GMAT Score:
770
Post Sat Oct 08, 2016 10:49 am
jmacym wrote:
One of my review questions...

The sum 7/8 + 1/9 is between...

The correct answer is (B) 3/4 and 1

The explanation is as follows: Since 1/9 < 1/8, 7/8 + 1/9 < 7/8 + 1/8 = 1 answer choices C, D, and E can be eliminated.
Since 7/8 > 6/8 = 3/4, 7/8 + 1/9 > 3/4 answer choice A can be eliminated. Thus, 3/4 < 7/8 + 1/9 < 1

Okay, so my thinking is first of all 7/8 + 1/9 is 71/72... obviously that was not even close to any of the answer choices.
The explanation confuses me even more because it's saying 1/9 is less than 1/8...which I understand how and why that is true, but 1/9 could be less than TONS of numbers. How am I supposed to know to use 1/8 instead of, lets say, 1/7 or 1/6, 1/5..etc. to get to the correct answer?
The idea is that (7/8) + (1/8) = 1. Because 1/9 < 1/8, it must be true that (7/8) + (1/9) < 1.

(In essence, 1/8 was chosen because it allowed you to easily see how the sum would compare to one.)

_________________
Veritas Prep | GMAT Instructor

Veritas Prep Reviews
Save $100 off any live Veritas Prep GMAT Course

  • +1 Upvote Post
  • Quote
  • Flag
Enroll in a Veritas Prep GMAT class completely for FREE. Wondering if a GMAT course is right for you? Attend the first class session of an actual GMAT course, either in-person or live online, and see for yourself why so many students choose to work with Veritas Prep. Find a class now!

GMAT/MBA Expert

Post Sat Oct 08, 2016 6:58 pm
Hi jmacym,

When posting a GMAT question, you should make sure to post the ENTIRE question (including the 5 answer choices). In many cases, the answer choices themselves provide a 'hint' as to how you can go about answering the question. The question that you're referring to includes the following answers:

The sum 7/8 + 1/9 is between?

A) 1/2 and 3/4
B) 3/4 and 1
C) 1 and 1 1/4
D) 1 1/4 and 1 1/2
E) 1 1/2 and 2

From the answer choices, we can see that there is no 'overlap' between any pair of consecutive answers, so we really just need to define the range. By extension, we likely do NOT need to do a perfect calculation to get to the correct answer (we can probably use a certain amount of estimation).

Since 6/8 = 3/4 = .75, we know that 7/8 has to be greater than .75 on its own.

7/8 + 1/8 would = 1, but since 1/9 < 1/8, then we're adding a number to .75 that will end up in a sum that is less than 1. We've now defined the range...

Final Answer: B

GMAT assassins aren't born, they're made,
Rich

_________________
Contact Rich at Rich.C@empowergmat.com

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Post Sat Oct 08, 2016 7:02 pm
jmacym wrote:
The sum 7/8 + 1/9 is between?

A) 1/2 and 3/4
B) 3/4 and 1
C) 1 and 1 1/4
D) 1 1/4 and 1 1/2
E) 1 1/2 and 2
7/8 + 1/8 = 1.
Since 1/9 is just a bit SMALLER than 1/8, 7/8 + 1/9 must be just a BIT LESS THAN 1.

The correct answer is B.

_________________
Mitch Hunt
GMAT Private Tutor
GMATGuruNY@gmail.com
If you find one of my posts helpful, please take a moment to click on the "UPVOTE" icon.
Available for tutoring in NYC and long-distance.
For more information, please email me at GMATGuruNY@gmail.com.

  • +1 Upvote Post
  • Quote
  • Flag
Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now.

GMAT/MBA Expert

Post Sun Oct 09, 2016 7:25 am
Quote:
The sum 7/8 + 1/9 is between

A)1/2 and 3/4
B)3/4 and 1
C)1 and 1 1/4
D)1 1/4 and 1 1/2
E)1 1/2 and 2
Well, first we know that 7/8 + 1/8 = 1
Since 1/9 is a little bit less than 1/8, we know that the sum 7/8 + 1/9 will be a little bit less than 1.
Since 7/8 is also greater than 3/4, the answer must be B

_________________
Brent Hanneson – Founder of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

Check out the online reviews of our course
Come see all of our free resources

  • +1 Upvote Post
  • Quote
  • Flag
GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!
Post Fri Apr 06, 2018 7:59 am
Quote:
The sum 7/8 + 1/9 is between

A)1/2 and 3/4
B)3/4 and 1
C)1 and 1 1/4
D)1 1/4 and 1 1/2
E)1 1/2 and 2
Notice that 1/9 is less than 1/8, so 7/8 + 1/9 < 7/8 + 1/8 = 1.

Furthermore, 7/8 itself is greater than 3/4 since 3/4 = 6/8.

Thus we see that the sum is between 3/4 and 1.

Alternate Solution:

Let’s add the two fractions, using 72 as the common denominator:

7/8 + 1/9 = 63/72 + 8/72 = 71/72.

We see that 71/72 is just slightly less than 1, so B is the obvious choice..

Answer: B

_________________
Jeffrey Miller Head of GMAT Instruction

  • +1 Upvote Post
  • Quote
  • Flag

Top First Responders*

1 GMATGuruNY 71 first replies
2 Rich.C@EMPOWERgma... 48 first replies
3 Brent@GMATPrepNow 37 first replies
4 Jay@ManhattanReview 26 first replies
5 ErikaPrepScholar 10 first replies
* Only counts replies to topics started in last 30 days
See More Top Beat The GMAT Members

Most Active Experts

1 image description GMATGuruNY

The Princeton Review Teacher

129 posts
2 image description Rich.C@EMPOWERgma...

EMPOWERgmat

116 posts
3 image description Jeff@TargetTestPrep

Target Test Prep

106 posts
4 image description Max@Math Revolution

Math Revolution

92 posts
5 image description Scott@TargetTestPrep

Target Test Prep

92 posts
See More Top Beat The GMAT Experts