Is x > 0 ?
(1) |x+3| < 4
(2) |x-3| < 4
OA E
Source: Veritas Prep
Is x > 0 ? (1) |x+3| < 4 (2) |x-3| < 4
This topic has expert replies
-
- Moderator
- Posts: 7187
- Joined: Thu Sep 07, 2017 4:43 pm
- Followed by:23 members
- fskilnik@GMATH
- GMAT Instructor
- Posts: 1449
- Joined: Sat Oct 09, 2010 2:16 pm
- Thanked: 59 times
- Followed by:33 members
Timer
00:00
Your Answer
A
B
C
D
E
Global Stats
$$x\,\mathop > \limits^? \,\,0$$BTGmoderatorDC wrote:Is x > 0 ?
(1) |x+3| < 4
(2) |x-3| < 4
Source: Veritas Prep
$$\,\left( {1 + 2} \right)\,\,\,\,\left\{ \matrix{
\,{\rm{Take}}\,\,x = 0\,\,\,\, \Rightarrow \,\,\,\left\langle {{\rm{NO}}} \right\rangle \,\, \hfill \cr
\,{\rm{Take}}\,\,x = 0.5\,\,\,\, \Rightarrow \,\,\,\left\langle {{\rm{YES}}} \right\rangle \,\, \hfill \cr} \right.\,\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,\,\,\left( {\rm{E}} \right)$$
This solution follows the notations and rationale taught in the GMATH method.
Regards,
Fabio.
Fabio Skilnik :: GMATH method creator ( Math for the GMAT)
English-speakers :: https://www.gmath.net
Portuguese-speakers :: https://www.gmath.com.br
English-speakers :: https://www.gmath.net
Portuguese-speakers :: https://www.gmath.com.br
GMAT/MBA Expert
- Brent@GMATPrepNow
- 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
Timer
00:00
Your Answer
A
B
C
D
E
Global Stats
When solving inequalities involving ABSOLUTE VALUE, there are 2 things you need to know:BTGmoderatorDC wrote:Is x > 0 ?
(1) |x+3| < 4
(2) |x-3| < 4
Rule #1: If |something| < k, then -k < something < k
Rule #2: If |something| > k, then EITHER something > k OR something < -k
Target question: Is x > 0 ?
Statement 1: |x+3| < 4
From Rule #1, we can write: -4 < x + 3 < 4
Subtract 3 from all 3 sides to get: -7 < x < 1
If -7 < x < 1, then:
x could equal 0.5, in which case the answer to the target question is YES, x IS greater than 0
x could equal -0.5, in which case the answer to the target question is NO, x is NOT greater than 0
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: |x-3| < 4
From Rule #1, we can write: -4 < x - 3 < 4
Add 3 to all 3 sides to get: -1 < x < 7
If -1 < x < 7, then:
x could equal 0.5, in which case the answer to the target question is YES, x IS greater than 0
x could equal -0.5, in which case the answer to the target question is NO, x is NOT greater than 0
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT
Statements 1 and 2 combined
IMPORTANT: Notice that I was able to use the same counter-examples to show that each statement ALONE is not sufficient. So, the same counter-examples will satisfy the two statements COMBINED.
In other words,
x could equal 0.5, in which case the answer to the target question is YES, x IS greater than 0
x could equal -0.5, in which case the answer to the target question is NO, x is NOT greater than 0
Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT
Answer: E
Cheers,
Brent