solve promptly ?

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solve promptly ?

by NSNguyen » Mon Dec 10, 2007 8:56 am
Q13:
If n is a positive integer, what is the remainder when 3^(8n+3) + 2 is divided by 5?
A. 0
B. 1
C. 2
D. 3
E. 4

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by sujaysolanki » Mon Dec 10, 2007 10:03 am
3^4 +3^4 + 3^3 = 1+1+7 = 9/5 = 4

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by hemanth28 » Mon Dec 10, 2007 10:07 am
units digits of power of 3 are
3,9,7,1,3,9,7,1.....
so units digit is repetative in multiples of 4

so for 3^(8n+3) ,units digit =(units digit of 3^(8n)) * (units digit of 3^3)

=7
add 2 and divide by 5 gives reminder of 4.

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by NSNguyen » Tue Dec 11, 2007 6:47 am
Thanks! :D
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