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# What is the units digit of (13)^4(17)^2(29)^3? (A) 9 (B) 7

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Intern
Joined: 30 Mar 2006
Posts: 27
Location: New Jersey
What is the units digit of (13)^4(17)^2(29)^3? (A) 9 (B) 7 [#permalink]

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07 Apr 2006, 05:54
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

What is the units digit of (13)^4(17)^2(29)^3?

(A) 9

(B) 7

(C) 5

(D) 3

(E) 1
_________________

Andre Crompton
andre.crompton@cit.com

Director
Joined: 06 Feb 2006
Posts: 897

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07 Apr 2006, 06:06

3*3*3*3= units digit 1

7*7= units digit 9

9*9*9= units digit 9

So....

9*9*1= units digit 1.
GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5043
Location: Singapore

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07 Apr 2006, 06:11
3^4 = 81
7^2 = 49
9^3 = 729

Units digit = 1*9*9 = 1
Manager
Joined: 25 Mar 2006
Posts: 129
Location: Stonybrook Univ

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07 Apr 2006, 06:59
clever ! thanks guys good thing to know. i had a question like this, took me a little while to do it my own ( not soo clever ) way

if lets say you had 2 find the 10's or 100's digit how would you do it ? would the same pattern work ?
Senior Manager
Joined: 29 Jun 2005
Posts: 403

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07 Apr 2006, 09:26
NTLancer wrote:
if lets say you had 2 find the 10's or 100's digit how would you do it ? would the same pattern work ?

Yes, it all depends on the number. You just have to learn the cycle
for example:
7^100 -
7^2 -.9
7^3 -.3
7^4 -.1
7^5 -.7
------
See the pattern, 7^..5 always has 7 unit digit.
7^10 -.7
------
7^50 -.7
------
7^100 -.7
07 Apr 2006, 09:26
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# What is the units digit of (13)^4(17)^2(29)^3? (A) 9 (B) 7

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