GMAT Prep - Number Line

This topic has expert replies
Source: — Problem Solving |

GMAT Instructor
Posts: 83
Joined: Sun Mar 02, 2008 9:05 pm
Thanked: 21 times
Followed by:2 members

by rey.fernandez » Sat Jun 28, 2008 10:00 pm
A. The solution to this inequality is x<1>1. Eliminate it because it's an unbounded set.

B. The solution to this one is x<=3. Eliminate it because it's an unbounded set.

C. The solution is x<4>4. Again, eliminate because it's an unbounded set.

D. Here, the solution is -5<x<-2 OR 2<x<5. While we have finite (or bounded) sets, unfortunately the question asks for exactly ONE such set, and this inequality has TWO. Eliminate.

E. Simplify:
2<=3x+4<=6
-2<=3x<=2
-2/3<=x<=2/3
This is clearly a single bounded set. The answer is E.
Rey Fernandez
Instructor
Manhattan GMAT

Master | Next Rank: 500 Posts
Posts: 215
Joined: Mon Apr 21, 2008 8:07 am

by rosh26 » Sun Jun 29, 2008 3:12 pm
Hi, thanks for the response...what is meant by a "bounded" set? unlcear of the actual term...thansl...

GMAT Instructor
Posts: 83
Joined: Sun Mar 02, 2008 9:05 pm
Thanked: 21 times
Followed by:2 members

by rey.fernandez » Sun Jun 29, 2008 8:22 pm
No problem. A bounded set is (roughly) one that has a start and an end. When you graph them on the number line, you get a line segment.
Examples of bounded sets:

-4<x<=7
-3<=x<=0

Unbounded sets are different in that in the positive direction or the negative direction or both directions, the set has no end... it extends out to infinity. When you graph unbounded sets, you get an infinitely long line or ray.
Examples of unbounded sets:
x<4>=7

HTH
Rey Fernandez
Instructor
Manhattan GMAT