solve promptly ?

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NSNguyen: Master | Next Rank: 500 Posts; Posts: 401; Joined: Fri May 04, 2007 9:21 amFollowed by: 1 member; Thanked: 3 times

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

waiting for your help.

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Source: Beat The GMAT — Problem Solving | Mon Dec 10, 2007 8:56 am

sujaysolanki: Master | Next Rank: 500 Posts; Posts: 214; Joined: Wed Nov 14, 2007 6:30 am; Thanked: 15 times

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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hemanth28: Master | Next Rank: 500 Posts; Posts: 157; Joined: Tue Dec 04, 2007 9:05 am; Thanked: 9 times; GMAT Score:680

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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NSNguyen: Master | Next Rank: 500 Posts; Posts: 401; Joined: Fri May 04, 2007 9:21 amFollowed by: 1 member; Thanked: 3 times

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

Thanks!

Please share your idea and your reasoning

https://bmnmed.com/home/
https://nguyensinguyen.vietnam21.org

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