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Source: — Data Sufficiency |
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Re: GMAT Prep 2 DS

by logitech » Tue Jan 13, 2009 7:52 pm
thechamp wrote:If zt < -3, Is z < 4?

1. z < 9

insuf

2. t < -4

t=-5 z=5

zt= -25 < -3

t=-5 z =2

zt=-10 < -3

INSUF

together still insuf E

But I really don't know how to solve this question easily with ineqs ?
LGTCH
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by thechamp » Tue Jan 13, 2009 8:02 pm
You are correct.

This is how I tried to solve it

For 2) t<-4

zt<-3
z < -3/t

Take any value of t<-4, z will always be < 4
e.g., If t=-8, z<-3/-8 i.e. 3/8 (< 4)
For t = -15, z<-3/-15 i.e z<1/5 (<4)

What am I missing?
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by cramya » Tue Jan 13, 2009 8:06 pm
For 2) t<-4

zt<-3
z < -3/t

Take any value of t<-4, z will always be < 4
e.g., If t=-8, z<-3/-8 i.e. 3/8 (< 4)
For t = -15, z<-3/-15 i.e z<1/5 (<4)

What am I missing?
Without knowing the sign of t it is not ok to rewrite inequality as

z<-3/t

If t was negative then the INEQUALITY reverses. This is the gotcha when dealing with inequalities.

Hope this helps!

Regards,
CR
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by logitech » Tue Jan 13, 2009 8:28 pm
cramya, what is your approach for this question ?
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by cramya » Tue Jan 13, 2009 8:34 pm
Picking numbers like u did seems to be a good option for this problem IMO

Algebrically it can get a bit tedious and nothing comes to my mind.



Regards,
CR
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