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:

(1) The tens digit of n is a factor of the units digit of n >

lets consider the number is 10X +y ; it says Y=kX.. so the number will becose 10X+KX = X (10 +k) which will be a composite number unless X=1 ; now X can not be 1 as 10X+Y> 20

also if you read this option properly the, number shoul be 10X+Y < 49

(1) The tens digit of n is a factor of the units digit of n.

If 9, factors are 9,3,1 = 19,39,99 If 8, factors are 8,4,2,1 = 18,28,48,88 If 7, factors are 7,1 = 17,77 If 6, factors are 6,3,2,1 = 16,26,36,66 If 5, factors are 5,1 = 15,55 If 4, factors are 4,2,1 = 14,24,44 If 3, factors are 3,1 = 13,33 If 2, factors are 2,1 = 12,22 If 1, factors are 1 = 11

None of the # above 20 are prime, so it is composite.

(1) The tens digit of n is a factor of the units digit of n. ex: any number greater than 20, and tens digit is a factor of the units digit. 24, 26, 28, 36,33....none r prime...so they have to be composite

So, A is sufficient

(2) The tens digit of n is 2. ex: 21,22,23,24,25....could be prime or composite

Good question indeed ... I decided the answer was C before reading through the solutions below... I guess I need to be more careful with DS ....
_________________

"You have to find it. No one else can find it for you." - Bjorn Borg