Timer
00:00
Answers
A
B
C
D
E
Stats
Difficulty—
What is the units digit of 18^47 ?
A. 0
B. 2
C. 4
D. 6
E. 8
OA B
Source: Magoosh
A. 0
B. 2
C. 4
D. 6
E. 8
OA B
Source: Magoosh
The units digit of 18^47 is the same as the units digit of 8^47.BTGmoderatorDC wrote:What is the units digit of 18^47 ?
A. 0
B. 2
C. 4
D. 6
E. 8
OA B
Source: Magoosh
Power cycle of 8:
8^1 = 8;
8^2 = ...4;
8^3 = ...2;
8^4 = ...6;
8^5 = ...8;
8^6 = ...4;
8^7 = ...2;
8^8 = ...6;
So the units digit of 8 in power cycle repeats a pattern of 4 numbers: 8, 4, 2, and 6
We have 18^47 = 18^(4*11 + 3)
Thus, the units digit of 18^47 would be the same as the units digit of 8^3 (ignoring 11 cycles of 4), which is 2.
The correct answer: B
Hope this helps!
-Jay
_________________
Manhattan Review GMAT Prep
Locations: GRE Manhattan | ACT Tutoring San Francisco | IELTS Prep Courses Austin | Seattle IELTS Tutoring | and many more...
Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.
