BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

What is the units digit of

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
Newbie | Next Rank: 10 Posts
Posts: 1
Joined: Sat Apr 04, 2020 12:20 am

Re: What is the units digit of

by Ast25 » Sat Apr 04, 2020 12:24 am
Unit digit of 5 raised to an odd power is 5 and unit digit of 16^6 is 6.
So 5-6= 9 is the answer
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members
Location: Vancouver, BC
Thanked: 5254 times
GMAT Score:770

Re: What is the units digit of

by Brent@GMATPrepNow » Sat Apr 04, 2020 5:35 am
BTGmoderatorDC wrote: ↑
Fri Apr 03, 2020 5:24 pm
 \(What\ is\ the\ units\ digit\ of\ 15^9\ -\ 16^6?\)

(A) 1
(B) 3
(C) 5
(D) 7
(E) 9


OA E

Source: Veritas Prep
If k is a positive integer, then the units digit of 15^k is always 5 (15^1 = 15, 15^2 = 225, 15^3 = 3375, 15^4 = ----5, etc)

If j is a positive integer, then the units digit of 16^j is always 6 (16^1 = 16, 16^2 = 256, 16^3 = 4096, 16^4 = ----6, etc)

So, 15^9 - 16^6 = (----5) - (---6) = ----9

Answer: E

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 8156
Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members
Location: Los Angeles, CA
Thanked: 43 times

Re: What is the units digit of

by Scott@TargetTestPrep » Sat Apr 25, 2020 1:35 pm
BTGmoderatorDC wrote: ↑
Fri Apr 03, 2020 5:24 pm
 \(What\ is\ the\ units\ digit\ of\ 15^9\ -\ 16^6?\)

(A) 1

(B) 3

(C) 5

(D) 7

(E) 9


OA E

Source: Veritas Prep
The units digit of 15^9 is equal to the units digit of 5^9. Recall that when 5 is raised to any positive integer power, the units digit of the number will always be 5. Similarly, when 16 (or, equivalently, 6) is raised to any positive integer power, the units digit of the number will always be 6.

15^9 has a units digit of 5, and 16^6 has a units digit of 6, so the units digit of 15^9 - 16^6 is 5 - 6 + 10 = 9 (notice that 5 - 6 = -1, but the units digit can’t be negative; since 15^9 is greater than 16^6, we can borrow a “1” from the tens digit of 15^9, i.e., adding a 10 to -1).

Answer: E

Scott Woodbury-Stewart
Founder and CEO
[email protected]

Image

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

ImageImage
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1