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

Redeem

To find the greatest value

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Legendary Member
Posts: 641
Joined: Tue Feb 14, 2012 3:52 pm
Thanked: 11 times
Followed by:8 members

To find the greatest value

by gmattesttaker2 » Thu Feb 06, 2014 10:59 pm
Hello,


Can you please tell me what would be the best approach to solve something like the following:


Which of the following is greatest?
(A) 6√7
(B) 9√4
(C) 7√6
(D) 6√8
(E) 8√5

OA: B

I eliminated A because D is greater than A.
B is 9 x 2 = 18
For C, D and E I was wondering if I need to take the square roots and then perform multiplication or if there is a better way to solve this problem. Thanks for your help - Sri
Top
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770

by Brent@GMATPrepNow » Thu Feb 06, 2014 11:17 pm
gmattesttaker2 wrote:
Which of the following is greatest?
(A) 6√7
(B) 9√4
(C) 7√6
(D) 6√8
(E) 8√5
One option is to take the integers in front of the roots and rewrite them as roots.
Then we'll use the fact that (√x)(√y)= √(xy)
I'll also use some general estimation. For example, (36)(7) is less than (40)(7) [aka 280]
So, √(36)(7) = √(some number less than 280)
Likewise, (81)(4) is greater than (80)(4) [aka 320]
So, √(81)(4) = √(some number greater than 320)
That's as precise as we need to be here.


Here's what I mean:
(A) 6√7 = (√36)(√7) = √(some number less than 280)
(B) 9√4 = (√81)(√4) = √(some number greater than 320)
(C) 7√6 = (√49)(√6) = √(some number less than 300)
(D) 6√8 = (√36)(√8) = √(some number less than 320)
(E) 8√5 = (√64)(√5) = √(320)

So, B must be the greatest

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
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 » Fri Feb 07, 2014 1:13 am
gmattesttaker2 wrote:
Which of the following is greatest?
(A) 6√7
(B) 9√4
(C) 7√6
(D) 6√8
(E) 8√5
An alternate approach is to SQUARE the answer choices:

(6√7)² = 36*7 = 252.
(9√4)² = 81*4 = 324.
(7√6)² = 49*6 = 294.
(6√8)² = 36*8 = 288.
(8√5)² = 64*5 = 320.

The greatest result is yielded by the option in red.

The correct answer is B.
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