Arithmetic Prob

Expert replies

selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Wed May 26, 2010 1:56 am

OG 12

As X increases from 165 to 166,which of the following must increase?

i)2x-5

ii)1-1/x

iii)1/(x^2-x)

A) i only

B)iii only

C)i and ii

d)i and iii

e) ii and iii

Like this post

Source: Beat The GMAT — Problem Solving | Wed May 26, 2010 1:56 am

liferocks: Legendary Member; Posts: 576; Joined: Sat Mar 13, 2010 8:31 pmFollowed by: 1 member; Thanked: 97 times

by liferocks » Wed May 26, 2010 2:02 am

since x is an integer and increases
2x-5 will increase

1/x will decrease and hence 1-1/x increase

x(x-1) increase..hence 1/(x^2-x) decrease

so ans C

"If you don't know where you are going, any road will get you there."
Lewis Carroll

Like this post

thephoenix: Legendary Member; Posts: 1560; Joined: Tue Nov 17, 2009 2:38 amFollowed by: 5 members; Thanked: 137 times

by thephoenix » Wed May 26, 2010 2:09 am

1) 2x-5 as x increases from 2x will inc for the given condition and therefore the value for 2x-5 will also inc
2) for the given condition 1/x decreases wrt to increasing value of x and therefore the value for 1-1/x will also inc
3)1/x(x-1) x(x-1) increases and the corresponding value of the exp dec

so only 1 and 2 are increasing C

Many of the great achievements of the world were accomplished by tired and discouraged men who kept on working

Like this post

frank1: Legendary Member; Posts: 537; Joined: Fri Jan 22, 2010 10:06 pmFollowed by: 1 member; Thanked: 14 times

by frank1 » Wed May 26, 2010 2:38 am

Time 1:51

IMO C

I think what is being test here is
people might start with x=165 and 166 and all(trap)
which will take lot of time...
rather than that...
if we do x=1...2...3
then it will be possible to solve it,with in 2 minutes....

Like this post

selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Wed May 26, 2010 4:21 am

Can we follow this method?

Instead of solving with the numbers given in prob,can we plug in another nums(like here 1...2...3) and solve?

Ur suggestions please...

Like this post

Patrick_GMATFix: GMAT Instructor; Posts: 1052; Joined: Fri May 21, 2010 1:30 amFollowed by: 98 members; Thanked: 335 times

by Patrick_GMATFix » Wed May 26, 2010 1:31 pm

@Selango,

Yes, you can plug in positive integers greater than 1. Generally when a question asks you how certain numbers behave, you can plug in other numbers that have similar behaviors. Along the number line, numbers can be divided into the following groups: {-infinity to -1} {-1 to 0} {0 to 1} and {1 to +infinity}

Instead of dealing with decimals between 165 and 166, you could deal with 2 or 3.

PS. The technique above wouldn't apply if the question is about even/odd of course, since that property divides numbers into different groupings.

This is OG12 # 176. A couple of ways to solve are attached.

-Patrick

Attachments

OG12-PS176.pdf: (64.78 KiB) Downloaded 100 times

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review