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# What is the units digit of 13^25*17^25?

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Math Expert
Joined: 02 Sep 2009
Posts: 58434
What is the units digit of 13^25*17^25?  [#permalink]

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01 Apr 2018, 10:32
00:00

Difficulty:

15% (low)

Question Stats:

89% (01:09) correct 11% (01:47) wrong based on 54 sessions

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What is the units digit of $$13^{25}*17^{25}$$?

(A) 0
(B) 1
(C) 3
(D) 7
(E) 9

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Joined: 15 Nov 2017
Posts: 169
Location: India
Concentration: Operations, Marketing
GPA: 4
WE: Operations (Retail)
Re: What is the units digit of 13^25*17^25?  [#permalink]

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01 Apr 2018, 10:37
Bunuel wrote:
What is the units digit of 13^25*17^25?

(A) 0
(B) 1
(C) 3
(D) 7
(E) 9

Cyclisity of 3 and 7 is 4, therefore $$3^1 * 7 ^1 = 21$$
Units digit is 1, Ans. B
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Re: What is the units digit of 13^25*17^25?  [#permalink]

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01 Apr 2018, 10:39
Bunuel wrote:
What is the units digit of 13^25*17^25?

(A) 0
(B) 1
(C) 3
(D) 7
(E) 9

units digit of 13^25*17^25=units digit of 3^25*7^25

by cyclicity of 3,unit digit of 3^25=3
by cyclicity of 7,unit digit of 7^25=7

So unit digit of 13^25*17^25=unit digit of 7*3=21=1

option B
Re: What is the units digit of 13^25*17^25?   [#permalink] 01 Apr 2018, 10:39
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