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What is the units' digit of (76)^k ?" (1) k is a prime

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Senior Manager
Joined: 21 Aug 2003
Posts: 258
Location: Bangalore
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What is the units' digit of (76)^k ?" (1) k is a prime [#permalink]  15 Nov 2003, 23:26
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"What is the units' digit of (76)^k ?"
(1) k is a prime integer
(2) k is greater than 2.

please explain your solution. That's the only way to understand the question
Manager
Joined: 26 Aug 2003
Posts: 233
Location: United States
Followers: 1

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

I vote for A.

Since every integer power of 6 results in 6 as the unit digit, it sufficient to know that k is an integer. Whereas Statement (2) doesn't tell us anything about what kind of number k is.
Intern
Joined: 10 Oct 2003
Posts: 45
Location: Finland
Followers: 1

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

I go with A too. The only case where the units digit is not 6 would be when k is 0 or k is a fraction.
Senior Manager
Joined: 21 Aug 2003
Posts: 258
Location: Bangalore
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Kudos [?]: 4 [0], given: 0

correct.
i was right in disagreeing with the official answer which was D.
thanks
Director
Joined: 13 Nov 2003
Posts: 793
Location: BULGARIA
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Kudos [?]: 27 [0], given: 0

Hallo Vicky think that the answer is correct, no matter what K is the units digit will always be 6...think makes sense P.S: In every case you have 6 multiplied by 6 which is ultimately 6( in units place) no matter what the power is
Intern
Joined: 11 Nov 2003
Posts: 30
Location: CA
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Kudos [?]: 0 [0], given: 0

I agree with BG.
I think asnwer is D
Director
Joined: 13 Nov 2003
Posts: 971
Location: Florida
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Kudos [?]: 32 [0], given: 0

whatever the power be, the unit digit will be "6". so it's D
Senior Manager
Joined: 30 Aug 2003
Posts: 325
Location: dallas , tx
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Kudos [?]: 9 [0], given: 0

How can it be A .. coz it states that k is prime ..but 6 is not a prime number....D is right..
_________________

shubhangi

Senior Manager
Joined: 21 Aug 2003
Posts: 258
Location: Bangalore
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Kudos [?]: 4 [0], given: 0

dear freinds.. u have missed one major pioint.
statement 1)
K is a prime number.
Thus whatever be the value of k =2,3,5...
Units digit of (76)^k will always be 6.

Satement 2)
K > 2 . If it was given that k is integer also, then definitely stat. 2 is also suffecient.
what if k = 2.5, 3.5 or any other fraction...!!

Thus 2 is not suffecient.

Hence Ans - A.

ps: Please be cautious in DS questions that involves variables x, y or k.
Check 1: Note down the domain of these variables - positive, negative, or just real numbers.
Check 2: Be sure to check each statement 1 & 2 for all possible values of these variables x, y within the above domain: positive, negative, fractions, underroots, etc...

thx
Manager
Joined: 26 Aug 2003
Posts: 233
Location: United States
Followers: 1

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

Hey Vicky,

Where did you find this problem? I hope it's not OG because this would show a major flaw on the ETS' part.
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