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The last digit of 18^47 is the same as the last digit of 8^47.

8^1=8; 8^2=64; 8^3=...2; 8^4=...6; 8^5=...8; ...

So the last digit of 8 in power repeats a pattern of 4 numbers: 8-4-2-6 --> 47=11*4+3, which means that the last digit of 8^47 will be the same as that of 8^3 (the third from the pattern), which is 2.

Re: What is the units digit of 18^47 ? [#permalink]

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25 Jul 2012, 02:35

B) 2

18^47 = (3^47) * (3^47) * (2^47)

Solving for units digit individually, we get unit's digit for 3^47 as 7 and of 2^47 as 8 (as 47/4 has remainder 3). Therefore, 7*7*8 has unit's digit 2.

Re: What is the units digit of 18^47 ? [#permalink]

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10 Dec 2014, 13:46

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Re: What is the units digit of 18^47 ? [#permalink]

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06 Jan 2015, 03:44

Hi,

Just sharing a thought. I haven't managed to understand how the difficulty of the questions is decided - not by you in the GMATCLUB, but by GMAC.

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