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:

First: 15x15=225. Then, you can see that 16x16 will not be enough.. Just to make sure. 17x17=289! The other squad we can guest that it is 18!
_________________

this ques is very eazy but difficult if don't know you perfect squares. I was able to get the first part very quick but I used calculator for the second part which is not allowed in the GMAT Exams

If you cannot remember the squares of the first 20 numbers I think the best approach is to play with the units digits only. The root of 324 should end to 2 or 8 and the root of 289 should end to 3 or 7. The next step is to take those figures in pairs and check the digit of their sum. So (2,3) --> units digit 5 (Answer D) (2,7) --> units digit 9 (No Answer) (8,3) --> units digit 1 (No Answer) (8,7) --> units digit 5 (Answer D) I don't even care about which numbers they actually are!

And it works for any number regardless if it is perfect square or not.

Thanks LU

What is this "Math formula" ? It works for any number? The square root of 64 + the square root of 25 is NOT equal to 64 - 25. Or what am I missing here?