BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

DS - Decimals and Ratio combined.

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Newbie | Next Rank: 10 Posts
Posts: 6
Joined: Fri Sep 09, 2011 5:04 am

DS - Decimals and Ratio combined.

by rajat27 » Wed Feb 20, 2013 10:35 pm
Any decimal that has only a Â…infnite number of nonzero digits is a terminating decimal. For example, 16, 0.73, and 3.178 are three terminating decimals. If m and n are positive integers and the ratio m/n is expressed as a decimal, is m/n a terminating decimal?
(1) 75 < m < 90
(2) n = 8

Please help me explain the logic ?

Thnx for help
Top
Source: — Data Sufficiency |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Wed Feb 20, 2013 11:05 pm
rajat27 wrote:Any decimal that has only a Â…infnite number of nonzero digits is a terminating decimal. For example, 16, 0.73, and 3.178 are three terminating decimals. If m and n are positive integers and the ratio m/n is expressed as a decimal, is m/n a terminating decimal?
(1) 75 < m < 90
(2) n = 8
Always remember that any fraction whose denominator has only 2 and/or 5 as prime factors can be expressed as a terminating decimal. Otherwise, for example if the denominator has 3 or 7 or 11 etc as its prime factor, then the fraction can not be expressed as a terminating decimal.

Statement 1: We don't know anything about the denominator. --> Not sufficient

Statement 2: As the denominator is only power of 2, the fraction can be expressed as terminating decimal irrespective of the numerator. --> Sufficient

The correct answer is B.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2095
Joined: Tue Dec 04, 2012 3:22 pm
Thanked: 1443 times
Followed by:247 members

by ceilidh.erickson » Thu Feb 21, 2013 11:33 am
Anurag is right, but it's also helpful to think about why this is true...

Our entire numerical system is based on 10s (because we have 10 fingers, and that's what cavemen started counting on). Every time we multiply or divide by a power of 10, we change the decimal placement:
0.001
0.01
0.1
1
10
100
1,000

When we divide by things that contain the factors of 10 (2 and 5), the decimal will resolve itself, because decimals are all based on 10s. Some power of 10 (100; 10,000; 100,000,000) will be divisible by that number. If it has any prime factors that don't go into 10 (3, 7, 11, etc), then we can say the decimals don't "like" it, because no power of 10 will ever be divisible by that number.
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
Top
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Thu Feb 21, 2013 11:54 am
Other problems that test the same concept:

https://www.beatthegmat.com/real-number- ... 61902.html
https://www.beatthegmat.com/terminating- ... 08208.html
https://www.beatthegmat.com/terminating- ... 92476.html
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Post new topic Post Reply
• Page 1 of 1