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

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Intern
Joined: 06 Oct 2010
Posts: 39
Followers: 0

Kudos [?]: 17 [0], given: 29

What is the units digit of 13^4*17^2*29^3? [#permalink]

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17 Oct 2010, 12:50
00:00

Difficulty:

15% (low)

Question Stats:

69% (01:36) correct 32% (00:41) wrong based on 200 sessions

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

(A) 9
(B) 7
(C) 5
(D) 3
(E) 1
[Reveal] Spoiler: OA

Last edited by Bunuel on 04 May 2015, 02:44, edited 1 time in total.
Renamed the topic and edited the question.
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Kudos [?]: 32 [4] , given: 2

Re: What is the units digit of 13^4*17^2*29^3? [#permalink]

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17 Oct 2010, 14:32
4
KUDOS
I think that the fastest and more important, the safest way to solve this is:
First brake the problem to three multiplication problems:
1. 13*13*13*13
2. 17*17
3. 29*29*29
In all of the problems we don't have to multiply by the whole number, but only by the last digit (because that is what we are asked about).
Second, simply multiply: 13*13*13*13. It is actually 3*3*3*3 (we are interested in the last digit). Thus - 3*3=9, 9*3=7(the last digit), 7*3=1 (the last digit).
17*17 is actually 7*7 = 9 (the last digit).
29*29*29 is actually -9*9*9- that can be interpreted into 9*9=1 (the last digit) and 1*9=9.
So eventually we will have- 9 (29^3) * 9 (17^2) * 1 (13^4). Therefore - 9*9=1(the last digit), 1*1=1

So the correct answer is E -1.
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Kudos [?]: 17 [0], given: 29

Re: What is the units digit of 13^4*17^2*29^3? [#permalink]

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17 Oct 2010, 17:03
Awesome! I think that explanation will help me solve a lot of "units digit" questions. Thanks!
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Kudos [?]: 1513 [1] , given: 235

Re: What is the units digit of 13^4*17^2*29^3? [#permalink]

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17 Oct 2010, 17:25
1
KUDOS
General rule :

To find the unit's digit- find the remainder when divided by 10.

to find the last two digits - find the remainder when divided by 100.

....and so on.

For advance theory of remainders check the Math book of gmat Club.
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Re: What is the units digit of 13^4*17^2*29^3? [#permalink]

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04 May 2015, 00:24
1
KUDOS
just need unit digit of every component and multipy them

3^1=3
3^2=9
3^3=7
3^4=1, it is first digit

7^2=9, it is second digit

9^3=9, it is third digit

1*9*9=1

E
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Re: What is the units digit of 13^4*17^2*29^3? [#permalink]

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12 May 2016, 10:49
Hello from the GMAT Club BumpBot!

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What is the units digit of 13^4*17^2*29^3? [#permalink]

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12 May 2016, 12:22
niheil wrote:
What is the units digit of 13^4*17^2*29^3?

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

Units digit of $$13^4$$ will be 1
Units digit of $$17^2$$ will be 9
Units digit of $$29^3$$will be 9

So, Units digit of $$13^4*17^2*29^3$$ will be 1 * 9 * 9 => 1

Answer will be option (E) 1

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What is the units digit of 13^4*17^2*29^3?   [#permalink] 12 May 2016, 12:22
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