The Powers that'll be

Expert replies

ashforgmat: Senior | Next Rank: 100 Posts; Posts: 71; Joined: Sun Feb 21, 2010 9:16 pm; Thanked: 3 times; GMAT Score:750

by ashforgmat » Mon Jan 03, 2011 1:29 am

Please can someone help me with the answer of this question ?
What is the unit's digit of the solution to :
(177)^28 - (133)^23

I know the technique just wanted to confirm the answer....
Thanks...

Like this post

Source: Beat The GMAT — Problem Solving | Mon Jan 03, 2011 1:29 am

Geva@EconomistGMAT: GMAT Instructor; Posts: 905; Joined: Sun Sep 12, 2010 1:38 amFollowed by: 123 members; Thanked: 378 times; GMAT Score:760

by Geva@EconomistGMAT » Mon Jan 03, 2011 1:35 am

ashforgmat wrote:Please can someone help me with the answer of this question ?
What is the unit's digit of the solution to :
(177)^28 - (133)^23

I know the technique just wanted to confirm the answer....
Thanks...

should be 4:
7 has a 4 place cycle: 7, 9, 3, 1. Since 28 is a multiple of 4, 177^28 will end with a 1.

by the same token, 3 has a 4-place cycle: 3, 9, 7, 1. 23 is "one less than" the nearest multipe of 4, so it's in the third place of the cycle: 7.

the units digit of the difference should then be ...1 - ...7 = ...4, in the same way that 11-7 is 4.

Geva
Senior Instructor
Master GMAT
1-888-780-GMAT
https://www.mastergmat.com

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review