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# What is the unit digit??

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What is the unit digit?? [#permalink]

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31 Oct 2009, 08:26
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Difficulty:

(N/A)

Question Stats:

40% (02:44) 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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Retired Moderator
Status: The last round
Joined: 18 Jun 2009
Posts: 1300
Concentration: Strategy, General Management
GMAT 1: 680 Q48 V34
Followers: 80

Kudos [?]: 1074 [0], given: 157

Re: What is the unit digit?? [#permalink]

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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]

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31 Oct 2009, 08:46
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.

Last edited by swatirpr on 31 Oct 2009, 09:02, edited 1 time in total.
Retired Moderator
Status: The last round
Joined: 18 Jun 2009
Posts: 1300
Concentration: Strategy, General Management
GMAT 1: 680 Q48 V34
Followers: 80

Kudos [?]: 1074 [0], given: 157

Re: What is the unit digit?? [#permalink]

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31 Oct 2009, 08:51

OA and OE will be posted later.
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Re: What is the unit digit?? [#permalink]

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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
Retired Moderator
Status: The last round
Joined: 18 Jun 2009
Posts: 1300
Concentration: Strategy, General Management
GMAT 1: 680 Q48 V34
Followers: 80

Kudos [?]: 1074 [0], given: 157

Re: What is the unit digit?? [#permalink]

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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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