Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

As zÂ² - 4z - 5 is the kind of a*x^2 + b*x + c where a is positive, thus (z-1)(z+5) > 0 is possible when z is not between the 2 roots : -1 and 5.

Hence, we know that z < -1 or z > 5

The question is a bit strange.... we cannot be sure here ... But as we have to choose, I take (E)

I get: z^2-4z-5>0 (z-5) (z+1)>0 z>5,z>-1

I do not understand the change in sign part. Pls explain.

We apply this rule :
> f(x) = a*x^2 + b*x + c where a is positive, f(x) > 0 when x is not between its roots if these roots exist.
> f(x) = a*x^2 + b*x + c where a is negative, f(x) > 0 when x is between its roots if these roots exist.

If we represent f(z)=z^2-4z-5 in XY plan, we obtain the fig1.

I also add u the representation of g(z)=-z^2-4z+5 to have the case with a <0 in the fig2.

Attachments

Fig1_a-postive.jpg [ 17.01 KiB | Viewed 559 times ]

Fig2_a-negative.jpg [ 16.88 KiB | Viewed 558 times ]

I got E for this one. My question is why is it this question an odd one ?? examining other choices, only x<-1 is one of the two solution. the other solution which is x>5 is not there and x> -5 or x>-1 range is too wide to make x always true.