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# What is the units digit of 2^39?

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Math Expert
Joined: 02 Sep 2009
Posts: 62637
What is the units digit of 2^39?  [#permalink]

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18 Feb 2020, 05:18
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Difficulty:

15% (low)

Question Stats:

80% (00:40) correct 20% (00:42) wrong based on 35 sessions

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What is the units digit of 2^39?

A) 2
(B) 4
(C) 6
(D) 8
(E) 9

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Re: What is the units digit of 2^39?  [#permalink]

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18 Feb 2020, 05:32
Bunuel wrote:
What is the units digit of 2^39?

(A) 2
(B) 4
(C) 6
(D) 8
(E) 9

2^39 ==> Cyclic order of 2 is 4

2^1=2
2^2=4
2^3=8
2^4=6
2^5=2
.
.
.
.
Here unit digit of 2^39==> 2^3==>8

Hence D
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Re: What is the units digit of 2^39?  [#permalink]

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29 Feb 2020, 12:43
Bunuel wrote:
What is the units digit of 2^39?

A) 2
(B) 4
(C) 6
(D) 8
(E) 9

Units digit of 2 (Cycle)
2
2*2=4
4*2=8
8*2=6
6*2=2
Repeat. So we have a cycle of 4.

To find unit digit of 2^39, we need to realise 36 out of 39 will be 9 cycles. The remainder is 3. And at third position of cycle we have 8.

So answer is Option D (8)

P.S: This is posted on Feb 29,2020. Let's see if I am around to come back to check this Post on Feb 29,2024.
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Re: What is the units digit of 2^39?   [#permalink] 29 Feb 2020, 12:43
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