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Source: — Problem Solving |

by vinay1983 » Sat Sep 07, 2013 12:49 am
Is it D?
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by ganeshrkamath » Sat Sep 07, 2013 5:06 am
sanjoy18 wrote:what is the reminder when 3^444+4^333 is divided by 5

A)0
B)1
C)2
D)3
E)4
All you need to do here is find the units digit of 3^444 and 4^333 to get to the answer.
Now units digits of powers of 3 follow a rule:
3^1 = 3
3^2 = 9
3^3 = 27
3^4 = 81
3^5 = 243
3^6 = __9
3^7 = __7
3^8 = __1
The pattern is : 3,9,7,1,3,9,7,1,....

A similar pattern for powers of 4 exists: 4,6,4,6,....

units digit of 3^444 = units digit of (3^4)^111 = 1

units digit of 4^333 = 4

1+4 = 5

So remainder when divided by 5 is 0.

Choose A

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by GMATGuruNY » Sat Sep 07, 2013 5:14 am
sanjoy18 wrote:what is the reminder when 3^444+4^333 is divided by 5

A)0
B)1
C)2
D)3
E)4
When an integer with a units digit of 3 is raised to successive powers, the units digits of the resulting integers repeat in a cycle of 4:
3, 9, 7, 1...3, 9, 7, 1...
Implication: when the exponent is a multiple of 4, the units digit of the resulting integer will be 1.
This, 3^444 has a units digit of 1.

When an integer with a units digit of 4 is raised to successive powers, the units digits of the resulting integers alternate between 4 and 6:
4, 6...4, 6...
Implication: when the exponent is odd, the units digit of the resulting integer will be 4.
Thus, 4^333 has a units digit of 4.

Thus, 3^444 + 4^333 = integer with a units digit of 1 + integer with a units digit of 4 = integer with a units digit of 5.
An integer with a units digit of 5 is a multiple of 5.
Since 3^444 + 4^333 is a multiple of 5, dividing it by 5 will yield a remainder of 0.

The correct answer is A.

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by vinay1983 » Sat Sep 07, 2013 7:37 am
My bad! Got the wrong answer, but happy that could follow the correct process for answering the question!
You can, for example never foretell what any one man will do, but you can say with precision what an average number will be up to!
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