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What is the unit digit??

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Hussain15
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What is the unit digit?? [#permalink] New post   31 Oct 2009, 08:26
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

40% (01:44) correct 60% (01:06) wrong based on 5 sessions
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What is the units digit of ( 6^15 - 7^4 - 9^3 )?
A) 8
B) 7
C) 6
D) 5
E) 4



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Re: What is the unit digit?? [#permalink] New post   31 Oct 2009, 08:41
I want to tag this post as "number properties" along with "powers". How can I do it?? :?
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Re: What is the unit digit?? [#permalink] New post   Updated on: 31 Oct 2009, 09:02
Hussain15 wrote:
What is the units digit of ( 6^15 - 7^4 - 9^3 )?
A) 8
B) 7
C) 6
D) 5
E) 4



Is OA "E" ?

Unit digit for term 6^15 = 6
Unit digit for term 7^4 = 1
Unit digit for term 9^3 = 9

altogether unit digit for ( 6^15 - 7^4 - 9^3 ) = 6 -1 -9 = 4

Thanks.

Originally posted by swatirpr on 31 Oct 2009, 08:46.
Last edited by swatirpr on 31 Oct 2009, 09:02, edited 1 time in total.
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Re: What is the unit digit?? [#permalink] New post   31 Oct 2009, 08:51
I will really appreciate your answers with explanation.

OA and OE will be posted later.
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gmattokyo
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Re: What is the unit digit?? [#permalink] New post   31 Oct 2009, 10:22
1
Kudos
swatirpr wrote:
Hussain15 wrote:
What is the units digit of ( 6^15 - 7^4 - 9^3 )?
A) 8
B) 7
C) 6
D) 5
E) 4



Is OA "E" ?

Unit digit for term 6^15 = 6
Unit digit for term 7^4 = 1
Unit digit for term 9^3 = 9

altogether unit digit for ( 6^15 - 7^4 - 9^3 ) = 6 -1 -9 = 4

Thanks.


I agree with your approach. But IMO ans is 6.(C)
just this last step... 6-1-9=6

take for example
436 (6^15 is bigger than other 2)
-71
-89
units digit=6-0=6
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Hussain15
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Re: What is the unit digit?? [#permalink] New post   01 Nov 2009, 00:25
Thanks for the input.

OA is "C".



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Re: What is the unit digit?? [#permalink]
01 Nov 2009, 00:25
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