remainder when xy is divided by 10

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abhi332: Master | Next Rank: 500 Posts; Posts: 117; Joined: Wed Dec 30, 2009 1:57 pmFollowed by: 1 member; Location: India; Thanked: 4 times

by abhi332 » Wed Feb 24, 2010 12:15 pm

If x = 3 ^ 21 and y = 6 ^ 55, what is the remainder when xy is divided by 10?

(A) 2

(B) 3

(C) 4

(D) 6

(E) 8

[spoiler]OA:E[/spoiler]

What you think, you become.

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Source: Beat The GMAT — Problem Solving | Wed Feb 24, 2010 12:15 pm

firdaus117: Master | Next Rank: 500 Posts; Posts: 102; Joined: Sat Feb 20, 2010 5:38 am; Location: IIM Ahmedabad; Thanked: 10 times

by firdaus117 » Wed Feb 24, 2010 12:58 pm

Dividing by 10 and getting the remainder is same as determining the unit's digit of xy.Now you can do it yourself,can't you?.

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abhi332: Master | Next Rank: 500 Posts; Posts: 117; Joined: Wed Dec 30, 2009 1:57 pmFollowed by: 1 member; Location: India; Thanked: 4 times

by abhi332 » Wed Feb 24, 2010 1:13 pm

Thanks firdaus117,

3 ^ 21 * 6 ^ 55
= ...3 * ...6
= ...8

so when divided by 10 will give 8 as the Ans

What you think, you become.

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