Events & Promotions
|
|
GMAT Club Daily Prep
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
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Apr 2601:30 AM EDT
-02:30 AM EDT
Learn how Keshav, a Chartered Accountant, scored an impressive 705 on GMAT in just 30 days with GMATWhiz's expert guidance. In this video, he shares preparation tips and strategies that worked for him, including the mock, time management, and more.
Apr 2610:00 AM EDT
-11:00 AM EDT
The Target Test Prep course represents a quantum leap forward in GMAT preparation, a radical reinterpretation of the way that students should study. Try before you buy with a 5-day, full-access trial of the course for FREE!
Apr 2512:30 AM EDT
-01:30 AM EDT
At one point, she believed GMAT wasn’t for her. After scoring 595, self-doubt crept in and she questioned her potential. But instead of quitting, she made the right strategic changes. The result? A remarkable comeback to 695. Check out how Saakshi did it.
Apr 2711:00 AM EDT
-12:00 PM EDT
Prefer video-based learning? The Target Test Prep OnDemand course is a one-of-a-kind video masterclass featuring 400 hours of lecture-style teaching by Scott Woodbury-Stewart, founder of Target Test Prep and one of the most accomplished GMAT instructors
Apr 2808:00 AM PDT
-11:00 AM PDT
Whether you are just beginning your MBA journey or fine-tuning your path to a 700+ score, GMAT Day is designed to give you a competitive edge.
May 0111:00 AM PDT
-12:00 PM PDT
Free- full-length test + 15 concept videos + 150+ short videos + study plan!
31 Mar 2021, 08:30
Kudos
Bookmarks
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
85% (01:00) correct
15%
(01:27)
wrong
based on 236
sessions
History
Date
Time
Result
Not Attempted Yet
If \(A_{n} = 7^n − 1\), what is the units digit of \(A_{33}\)?
A. 1
B. 3
C. 6
D. 7
E. 9
A. 1
B. 3
C. 6
D. 7
E. 9
Asked: If \(A_{n} = 7^n − 1\), what is the units digit of \(A_{33}\)?
\(A_{33} = 7^{33} -1\)
Unit digit of 7^1 = 7
Unit digit of 7^2 = 9
Unit digit of 7^3 = 3
Unit digit of 7^4 = 1
Unit digit of 7^5 = 7
Unit digit of 7^n has cyclicity of 4.
Unit digit of 7^33 = Unit digit of 7^{8*4+1} = Unit digit of 7^1 = 7
Unit digit of 7^33 - 1 = 6
IMO C
\(A_{33} = 7^{33} -1\)
Unit digit of 7^1 = 7
Unit digit of 7^2 = 9
Unit digit of 7^3 = 3
Unit digit of 7^4 = 1
Unit digit of 7^5 = 7
Unit digit of 7^n has cyclicity of 4.
Unit digit of 7^33 = Unit digit of 7^{8*4+1} = Unit digit of 7^1 = 7
Unit digit of 7^33 - 1 = 6
IMO C
31 Mar 2021, 08:39
Kudos
Bookmarks
Bunuel
The question finally requires us to find the units digits of \(7^{33}-1\)
Quick answer: \(7^{33}-1\) is odd-odd, which becomes even.
Only C is even.
Method:
7 has a cyclicity of 4 of units digit when its powers are increased.
Cyclicity: 7, 9, 3, 1, 7...
\(7^{33}-1=7^{32-1}-1\)
\(7^{32-1} \) will have same units digit as 7^1 or 7.
Thus our answer for \(7^{33}-1\) is 7-1 or 6
C
