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

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

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New post 24 Mar 2011, 17:56
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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

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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
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Re: unit digit [#permalink]

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New post 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
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Joined: 01 Feb 2011
Posts: 726

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

Re: unit digit [#permalink]

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New post 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 .

Answer C.

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

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Re: unit digit [#permalink]

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New post 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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New post 20 Sep 2016, 15:01
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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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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