OG Q194

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kaf: Senior | Next Rank: 100 Posts; Posts: 53; Joined: Mon Feb 09, 2009 12:18 am; Thanked: 1 times

by kaf » Tue Mar 24, 2009 9:32 am

Please i would like someone to explain to me how this works.I found this question in OG

What is the units digit of (13)^4(17)^2(29)^3

I saw the explanation in OG but i would to find out if someone has
an alternative for solving this question quicker

thanks

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Source: Beat The GMAT — Problem Solving | Tue Mar 24, 2009 9:32 am

DanaJ: Site Admin; Posts: 2567; Joined: Thu Jan 01, 2009 10:05 amFollowed by: 550 members; Thanked: 712 times; GMAT Score:770

by DanaJ » Tue Mar 24, 2009 9:37 am

In order to find the units digit of this number you must first find the units digits of its components.
1. 13^4 - its units digit will be the units digit of 3^4 = 81 - so it's 1 for this one

2. 17^2 - its units digit will be the units digit of 7^2 = 49 - it's 9 for this number

3. 29^3 - its units digit will be the units digit of 9^3 = 729 - it's 9 again.

The units digit of the whole number will be the units digit of the product of the 3 units digit discovered above: 1*9*9 = 81 - units digit 1.

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