OG 2nd Edition Q58

This topic has expert replies
Source: — Problem Solving |

User avatar
Master | Next Rank: 500 Posts
Posts: 101
Joined: Sun Sep 26, 2010 9:33 am
Thanked: 5 times

by jaxis » Sun Feb 06, 2011 8:06 am
quaktar0004 wrote:Can someone please help me with this problem? There has to be a faster method than the explanation given.

31/125 =

a. 0.248
b. 0.252
c. 0.284
d. 0.312
e. 0.320
Multtiply the numerator and denominator by 8

248/1000.

Junior | Next Rank: 30 Posts
Posts: 11
Joined: Sat Jan 15, 2011 3:40 pm

by quaktar0004 » Sun Feb 06, 2011 8:36 am
Thank you for the quick response. Just curious...how did you determine that 8 was the right # to multiply both the numerator and denominator by?

User avatar
Master | Next Rank: 500 Posts
Posts: 101
Joined: Sun Sep 26, 2010 9:33 am
Thanked: 5 times

by jaxis » Sun Feb 06, 2011 8:41 am
quaktar0004 wrote:Thank you for the quick response. Just curious...how did you determine that 8 was the right # to multiply both the numerator and denominator by?
try to make he denominator a power of 10 in these kind of problems.

In this case 125 can be converted to closest power of 10 by multiplying it with 8.

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 » Sun Feb 06, 2011 8:58 am
quaktar0004 wrote:Can someone please help me with this problem? There has to be a faster method than the explanation given.

31/125 =

a. 0.248
b. 0.252
c. 0.284
d. 0.312
e. 0.320
Another approach:

Since 30/120 = 1/4, we know that the correct answer must be around .25. Eliminate C, D and E.

Now compare 31/125 to 1/4 to see which is larger. To compare fractions, we multiply the denominator in each fraction by the numerator in the other. The numerator that yields the bigger product will belong to the bigger fraction:

4*31 = 124.
125*1 = 125.

Since the numerator of 1/4 yields the bigger product, 1/4 is bigger than 31/125. Thus, the correct answer must be less than 1/4 = .25.

The correct answer is A.
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

Junior | Next Rank: 30 Posts
Posts: 11
Joined: Sat Jan 15, 2011 3:40 pm

by quaktar0004 » Sun Feb 06, 2011 10:18 am
THank you both for great explanations!