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# What is the unit digit of (2) ^29 * (5) ^29 * (7) ^29?

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Senior Manager
Joined: 02 Jan 2017
Posts: 307
What is the unit digit of (2) ^29 * (5) ^29 * (7) ^29?  [#permalink]

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17 Mar 2017, 00:46
00:00

Difficulty:

5% (low)

Question Stats:

90% (01:16) correct 10% (00:39) wrong based on 40 sessions

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What is the unit digit of (2) ^29 * (5) ^29 * (7) ^29?

A) 1

B) 5

c) 9

D) 0

E) 7

Source: www.f1gmat.com
Senior Manager
Joined: 24 Apr 2016
Posts: 331
Re: What is the unit digit of (2) ^29 * (5) ^29 * (7) ^29?  [#permalink]

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17 Mar 2017, 11:34
In the given expression we see that it has 2 * 5, which makes the units digit as 0.

Manager
Joined: 14 Oct 2015
Posts: 249
GPA: 3.57
What is the unit digit of (2) ^29 * (5) ^29 * (7) ^29?  [#permalink]

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20 Mar 2017, 12:43
i got this right but can someone please explain this in detail on how to approach this.

Edit: So i figured 5 ^ anything is in 5 and 2 ^ anything will end in either 2, 4, 6, 8 and this multiplied by 5 is always going to end in a number with 0 as its unit digit. That multiplied by any power of 7 will still have 0 intact in the unit digit.
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Senior Manager
Joined: 24 Apr 2016
Posts: 331
What is the unit digit of (2) ^29 * (5) ^29 * (7) ^29?  [#permalink]

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20 Mar 2017, 12:55
1
jedit

Let me put the question in a simpler way.

What is the unit's digit of 2 * 5 * 7

Clearly we know that 2*5 is 10. Now when we multiple 7 to 10, we know the unit's digit will be 0. Or if we multiple any integer with 10, the unit's digit will still be 0.

So in the above question (2) ^29 * (5) ^29 * (7) ^29, we can clearly see that there is 5*2 forming a 10. Now whatever gets multiplied to that 10, the unit's digit will remain as 0.

Does it help?
Director
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Joined: 05 Jan 2017
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Location: India
Re: What is the unit digit of (2) ^29 * (5) ^29 * (7) ^29?  [#permalink]

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21 Mar 2017, 02:37
vikasp99 wrote:
What is the unit digit of (2) ^29 * (5) ^29 * (7) ^29?

A) 1

B) 5

c) 9

D) 0

E) 7

Source: http://www.f1gmat.com

there is 2 and there is 5. hence the unit digit will be 0
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Re: What is the unit digit of (2) ^29 * (5) ^29 * (7) ^29? &nbs [#permalink] 21 Mar 2017, 02:37
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