Questions about the world of GRE Math from other sources and general math related questions.
krypen
Forum Guests
 
Posts: 1
Joined: Fri Nov 29, 2013 11:42 am
 

simple inequality

by krypen Fri Nov 29, 2013 6:55 pm

In the 5 lb book of problems, #22 on page 383:

|3 + 3x| < -2x

A B
--- ---
|x| 4

I solved the inequality like this:
3 + 3x < -2x
5x < -3
x < -3/5

or

3 + 3x > 2x
x > -3

Giving me an answer of:
x < -3/5 OR x > -3

But according to the answer in the book, it shows:
-3 < x < -3/5

which means that x > -3 AND x < -3/5.

Why AND and not OR in this case?
tommywallach
Manhattan Prep Staff
 
Posts: 1917
Joined: Thu Mar 31, 2011 11:18 am
 

Re: simple inequality

by tommywallach Fri Nov 29, 2013 9:22 pm

Hey Krypen,

Well, the other reading wouldn't make any sense. It can't be one or the other--just try plugging in values outside of the relevant range! You can't solve an equation to two contradictory answers!

-t