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 350,000 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:

Re: What is the units digit of a^18? [#permalink]
10 Dec 2012, 04:14

1

This post received KUDOS

Marcab wrote:

Statement 1 tells us that the number may be either 3 or 7. Insufficient. Statement 2 confirms that the number is 3. So last digit of 3^18 is the same as the last digit of 3^2 , which is 9. Hence sufficient. +1 B

Hi Marcab

I have a question and I could be wrong but

lets take A a^2 has a units digit of 9 As you pointed out that the unit digit of a can be 3 or 7 but the question is asking for unit's digit of a^18. Lets take 3 and 7 seperately 3 units digit - 3, 9, 7, 1, 3, ..... therefore, the units digit for 3^18 is 9 7 units digit - 7, 9, 3, 1, 7, ... therefore, the units digit for 7^18 is 9 too. Thus, SUFFICIENT

2nd statement is clearly sufficient. Therefore, correct answer should be D.

Please let me know if the above explanation is wrong.

Re: What is the units digit of a^18? [#permalink]
09 Dec 2012, 18:45

Expert's post

Statement 1 tells us that the number may be either 3 or 7. In either case we will get 9 as the answer. Sufficient. Statement 2 confirms that the number is 7. So last digit of 7^18 is the same as the last digit of 7^2 , which is 9. Hence sufficient. +1 D _________________

Re: What is the units digit of a^18? [#permalink]
10 Dec 2012, 03:45

Ans: we need to find the value of a to get the unit digit, looking at (1) we find that a could be 3 or 7, looking at (2) we find that a is 7 ( the units digit cyclicity is 2 or 4) and only 7 gives a units digit as 3 at raised to power 7. So the answer is (B) _________________

Re: What is the units digit of a^18? [#permalink]
10 Dec 2012, 04:43

Expert's post

Hii sjai. Kudos to you. I am not at all a morning guy and this question is simply restates the fact. Sorry for the confusion and thanks. _________________

Re: What is the units digit of a^18? [#permalink]
10 Dec 2012, 05:42

deepri0812 wrote:

Answer is D , but why is the official answer B ?

D => if each answer is sufficient answer <1> is not sufficient, as there are two answers 3 and 7. it needs to have one answer to be sufficient, hence =>B

Re: What is the units digit of a^18? [#permalink]
11 Dec 2012, 04:37

apoorvarora wrote:

What is the units digit of a^18?

(1) a^2 has a units digit of 9 (2) a^7 has a units digit of 3

Ans: : We need to find a to find the units digit. From statement 1 we get a to be either 3 or 7. From statement 2 we get a to be 7( checking the cyclicity of numbers we find that only 7 has unit digit 3 at power 7). Therefore the answer is (B). _________________

Re: What is the units digit of a^18? [#permalink]
11 Dec 2012, 04:42

Expert's post

priyamne wrote:

apoorvarora wrote:

What is the units digit of a^18?

(1) a^2 has a units digit of 9 (2) a^7 has a units digit of 3

Ans: : We need to find a to find the units digit. From statement 1 we get a to be either 3 or 7. From statement 2 we get a to be 7( checking the cyclicity of numbers we find that only 7 has unit digit 3 at power 7). Therefore the answer is (B).

Units digit of 3^18 and units digit of 7^18 are the same. Both statements are sufficient. _________________

Type of Visa: You will be applying for a Non-Immigrant F-1 (Student) US Visa. Applying for a Visa: Create an account on: https://cgifederal.secure.force.com/?language=Englishcountry=India Complete...