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I have a vague idea about this and took a guess and got it [#permalink]

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06 Nov 2006, 07:03

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I have a vague idea about this and took a guess and got it right. But I'd like to see some other explanations

I basically thought of since its exponent is an odd number, its last digit will always be odd and then tried seeing a pattern and picked 7 coz if you multiple it 7 times, gets you last digit 7......

3^1 = 3, 3^2 = 9, 3^3 = 27, 3^4 = 81, 3^5 = 243 and now the ones digit starts repeating. [edit original answer to make more clear]

so the sequence is {3,9,7,1,3,9,7,1,3,9,7,1, ....} so we merely have to find the 987th one in the series. Apparently, each fourth term is a 1 (so term 8 is 1, term 12 is 1, etc..). That means term 984 is a 1, term 985 is a 3, term 986 is a 9, and term 987 is a 7.

powers of3 go in seq of 1,3,9,7...
follow it..u get 7

quote="uvs_mba"]I have a vague idea about this and took a guess and got it right. But I'd like to see some other explanations

I basically thought of since its exponent is an odd number, its last digit will always be odd and then tried seeing a pattern and picked 7 coz if you multiple it 7 times, gets you last digit 7......