PS Patterns

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qazpt: Newbie | Next Rank: 10 Posts; Posts: 9; Joined: Thu Dec 10, 2009 3:04 pm; Thanked: 2 times

by qazpt » Fri Dec 11, 2009 12:54 pm

If 27^20 is multiplied out, what is the units digit?

no answer given

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Source: Beat The GMAT — Problem Solving | Fri Dec 11, 2009 12:54 pm

ace_gre: Senior | Next Rank: 100 Posts; Posts: 98; Joined: Mon Nov 23, 2009 2:30 pmFollowed by: 1 member; Thanked: 26 times

by ace_gre » Fri Dec 11, 2009 1:35 pm

7^1=7
7^2=49
7^3=343
7^4=...1

7^5=7
..

repeating patterns.
7^20=7^(4x)= units digit is 1.

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