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Hyperstorm
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GMATprep DS question 08 Oct 2007, 23:39
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Please explain the solution to the following:

What is the remainder when 3^(4n+2) + M is divided by 10?

1. N=2
2. M=1



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GMATprep DS question 09 Oct 2007, 00:31
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(C) for me :)

3^(4n+2) + M is divided by 10?

In order to respond, we need to know the unit digit of ( 3^(4n+2) + M ).

Notice that 4*n+2 provides a number such as -10, -6, 2, 6, 10 if it is an integer. But, nothing states that N and M are integers.

So, no need to search a pattern for 3^(4n+2) [and then by knowing M, we could eventually conclude].

We have to know both N & M to conclude.
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GMATprep DS question 09 Oct 2007, 02:13
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Hyperstorm
Please explain the solution to the following:

What is the remainder when 3^(4n+2) + M is divided by 10?

1. N=2
2. M=1
Show more


(1) => 3^10 + M
last digit of 3^10 is 9, so remainder will depend on value of M. INSUFF
(2) INSUFF as we don't know value of N.

From (1) & (2) remainder = 0 SUFF

Ans C.
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GMATprep DS question 09 Oct 2007, 03:11
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Hyperstorm
Please explain the solution to the following:

What is the remainder when 3^(4n+2) + M is divided by 10?

1. N=2
2. M=1
Show more


That is relatively easy.

There is a cycle wnen we count a power of three.
3^2 = 9
3^3 = 27
3^4 = 81
3^5 = 243

Numbers 9,7,1,3 (units digit) will be repeated every 4 powers. Therefore, let's try n equal 1,2,3,4. Every time units digit will equal 9, since we have powers 6, 10, 14, 18 and so on. :) As we know the units digit of the first number, we only need to know the units digit of the second one.

The answer is B.
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GMATprep DS question 09 Oct 2007, 03:22
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Manny Calavera
Hyperstorm
Please explain the solution to the following:

What is the remainder when 3^(4n+2) + M is divided by 10?

1. N=2
2. M=1

That is relatively easy.

There is a cycle wnen we count a power of three.
3^2 = 9
3^3 = 27
3^4 = 81
3^5 = 243

Numbers 9,7,1,3 (units digit) will be repeated every 4 powers. Therefore, let's try n equal 1,2,3,4. Every time units digit will equal 9, since we have powers 6, 10, 14, 18 and so on. :) As we know the units digit of the first number, we only need to know the units digit of the second one.

The answer is B.
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What if n=-2? :)

and Welcome to GMATClub ! :D :)
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Manny Calavera
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GMATprep DS question 09 Oct 2007, 03:43
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Fig


What if n=-2? :)

and Welcome to GMATClub ! :D :)
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Hmm. You got the point here. There is no data that n is positive or that it is not a fraction. Then the answer is C.

Thanks for the welcoming. :)I will try to improve not only math but also English here. It still leaves much to be desired.
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GMATprep DS question 09 Oct 2007, 03:54
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Manny Calavera
Fig


What if n=-2? :)

and Welcome to GMATClub ! :D :)

Hmm. You got the point here. There is no data that n is positive or that it is not a fraction. Then the answer is C.

Thanks for the welcoming. :)I will try to improve not only math but also English here. It still leaves much to be desired.
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U have found the right place for both.... Good Luck ! :)
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GMATprep DS question 09 Oct 2007, 07:16
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OA is B -- not sure the original question specified n to be positive... if anyone else if familiar with this problem please chime in.

Thanks for the explanation, Manny! They always seem easy once you see the right solution =)
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Manny Calavera
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GMATprep DS question 09 Oct 2007, 10:48
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Hyperstorm
OA is B -- not sure the original question specified n to be positive... if anyone else if familiar with this problem please chime in.

Thanks for the explanation, Manny! They always seem easy once you see the right solution =)
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You're welcome. :))

That is strange, about B, I mean. May be this is an experimental question? Sure, this is too simple for a hard task, and there is a hidden trick, but even with this 3-cycle trick the answer is C.
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GMATprep DS question 10 Oct 2007, 13:45
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Hyperstorm
Please explain the solution to the following:

What is the remainder when 3^(4n+2) + M is divided by 10?

1. N=2
2. M=1
Show more


I get C.

1: N =2. If M=1 R=1, if M=2 R=2 Insuff.

2: If N=1 R=7 If n=2 R=1.

Together we know N and M so this is suff.


How is B the OA???



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Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
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