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# If a^b=c, what is the units digit of c?

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Intern
Joined: 24 Jul 2006
Posts: 4

Kudos [?]: 2 [0], given: 20

If a^b=c, what is the units digit of c? [#permalink]

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24 Mar 2011, 17:56
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Difficulty:

45% (medium)

Question Stats:

56% (00:41) correct 44% (00:44) wrong based on 98 sessions

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Hey guys,

How would you solve the following DS question:

If a^b=c, what is the units digit of c?

1. a^2 – 36 = 0
2. b is a positive integer.

Thanks
[Reveal] Spoiler: OA

Kudos [?]: 2 [0], given: 20

Director
Status: Impossible is not a fact. It's an opinion. It's a dare. Impossible is nothing.
Affiliations: University of Chicago Booth School of Business
Joined: 03 Feb 2011
Posts: 872

Kudos [?]: 389 [0], given: 123

Re: unit digit [#permalink]

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24 Mar 2011, 18:04
1. Insufficient.
b is not known.
If b = 0 then the answer is 1
If b>0 then the answer is 6

2. Insufficient

1) + 2) Sufficient.
a = -6 or +6 and b > 0
The answer is 6

CAUTION : The catch here b should be "integer" which is true from 2)

rait_m wrote:
Hey guys,

How would you solve the following DS question:

If a^b=c, what is the units digit of c?

1. a^2 – 36 = 0
2. b is a positive integer.

Thanks

Kudos [?]: 389 [0], given: 123

Director
Joined: 01 Feb 2011
Posts: 726

Kudos [?]: 140 [0], given: 42

Re: unit digit [#permalink]

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24 Mar 2011, 19:08
1. Not sufficient
As we dont know anything about b ,its not possible to determine a^b

2. Not sufficient

Here we dont know anything about a.so its not possible to determine a^b

together we know

a = +6 or a = -6 and b is positive integer,

this is enough to say c = 6 .

Kudos [?]: 140 [0], given: 42

Director
Status: No dream is too large, no dreamer is too small
Joined: 14 Jul 2010
Posts: 624

Kudos [?]: 1113 [0], given: 39

Re: unit digit [#permalink]

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25 Mar 2011, 06:38
rait_m wrote:
Hey guys,

How would you solve the following DS question:

If a^b=c, what is the units digit of c?

1. a^2 – 36 = 0
2. b is a positive integer.

Thanks

(1) a= ±6, nothing about b. if b =0 unit digit will 1, and b= 1 unit digit will 6 Insuff.
(2) b is positive so b>0, any power of 6 gives 6 as unit digit.
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Re: If a^b=c, what is the units digit of c? [#permalink]

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20 Sep 2016, 15:01
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Re: If a^b=c, what is the units digit of c?   [#permalink] 20 Sep 2016, 15:01
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# If a^b=c, what is the units digit of c?

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