If zt

Question

If zt < -3, is z < 4?

(1) z < 9
(2) t < -4

Bunuel · Accepted Answer

Number picking would probably be the most efficient way to attack this problem. Even when we consider both statements together we can easily find two sets of numbers which give us different answers to the question whether z<4:

If z=5 and t=-5 (zt=-25<-3) the answer is NO;
If z=1 and t=-5 (zt=-5<-3) the answer is YES.

Answer: E.

netrix · Answer

With a) we don't now nothing about t and z could be < 4 or >=4 and < 9 so INSUF
b) we don't now nothing about z, z could be or not less than 4

Now together: 
if z = 5 and t <-4 it is true that zt < -3
however if z= 3 it is also true that zt< -3
so it must be E

I hope you find useful my explanation

kuttingchai · Answer

Vote for E

i did it this way

(A) when Z < 9

if (Z = 8 and t = -1/2)

zt < -3 = true

Z < 4 (NO)

if (Z = 2 and t = -1/2)

zt < -3 = true

Z < 4 (Yes)

Data not sufficient

----------------------------

(B) t < -4

if (Z = 8 and t = -5)

zt < -3 = true

Z < 4 (NO)

if (Z = 2 and t = -5)

zt < -3 = true

Z < 4 (Yes)

Data not sufficient

-----------------------------

(C) combine when Z < 9 and t < -4

if (Z = 8 and t = -5)

zt < -3 = true

Z < 4 (NO)

if (Z = 2 and t = -5)

zt < -3 = true

Z < 4 (Yes)

Data not sufficient

there for E

NoHalfMeasures · Answer

Hi Bunuel and other experts,

When you do this(number picking) it seems so simply! However, number picking is my Achilles' Heel. It is just so frustratingly difficult for me to come up with right numbers.

When I micro-analyze my thinking process while I try to come up with right values to show counter examples this is what I see: I first need to ensure z <9 and then make sure that t < -4 and then ensure that zt< -3 with the aim of getting a NO for z<4. Even though I am using 'then' after every decision, the fact is- to generate right values, you essentially need to make these 4 decisions simultaneously. I simply dont know how I can do this in 20-30 seconds without befuddling my short term memory apparatus. I am saying 20-30 secs as in most of the hard questions you will have to rule out st-A, st-B and A+B. thus you will make 5-6 such decisions for every question.

When I solve such questions I am either totally flustered or take more than 4 mins. Are there efficient ways to do this and which will work for most of the hard problems (inequality, modulus, reciprocal, neg/pos and their combination) etc..in less than 2-3 mins? 
Thanks!

david12345 · Answer

zt < -3 implies either z>0 and t<0 or z<0 and t>0 (1) we ain't told anything abt t... Also, z can be 2 or 4 producing a Y/N cases (2) at least we know t is <0; but we dont know whether z>4 or <4. Both alone insufff. Taken together, tsst: z=2, t=-5 we get zt = -10 (<-3) Response to stem is Yes, z < 4 Also, take z=4 and t=-5 we get zt = -20 (<-3) Response is No z is not < 4. So, E should be OA.

thangvietnam · Answer

i missed this question.
this test a basic point
t<-4 so we divide both side by t and change the way of equality
zt<-3
z>-3/t=-3/-4=3/4
insufficient.

SchruteDwight · Answer

zt<-3 \ \cap \ z<4   \implies z(t+1)<1

Combining \ both \ statements:

z=8, t=-5 \implies 8(-5)<1 \implies (YES)

z=-9, t=-5 \implies -8(-5)<1 \implies (NO)

Anjali_1453 · Answer

Can someone explain why B is insufficient ? When we plug t= -4 we get z is less than 0.75 ans the value will further reduce decreasing value of t, which is definitely less than 4 ? Am I missing something?

Bunuel · Answer

If z=5 and t=-5 (zt=-25<-3) the answer is NO; 
 If z=1 and t=-5 (zt=-5<-3) the answer is YES.

Answer: E.

P.S. Pure algebraic questions are no longer a part of the  DS syllabus  of the GMAT.

DS questions in GMAT Focus encompass various types of word problems, such as:

Word Problems 
 Work Problems 
 Distance Problems 
 Mixture Problems 
 Percent and Interest Problems 
 Overlapping Sets Problems 
 Statistics Problems 
 Combination and Probability Problems

While these questions may involve or necessitate knowledge of algebra, arithmetic, inequalities, etc., they will always be presented in the form of word problems. You won’t encounter pure "algebra" questions like, "Is x > y?" or "A positive integer n has two prime factors..."

Check  GMAT Syllabus for Focus Edition

You can also visit the  Data Sufficiency forum  and filter questions by  OG 2024-2025, GMAT Prep (Focus), and Data Insights Review 2024-2025 sources  to see the types of questions currently tested on the GMAT.

So, you can ignore this question.

Hope it helps.

If zt < -3, is z < 4 ? (1) z < 9 (2) t < -4

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GMAT Data Sufficiency (DS) Questions

If zt < -3, is z < 4 ? (1) z < 9 (2) t < -4

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