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Number Theory Level pending

What is the units digit of the product 2 2015 × 7 2015 2^{2015} \times 7^{2015} ?


The answer is 4.

Andrew The by Andrew The , 25, USA

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1 solution

Ashwin Padaki
May 17, 2015

2 2015 2^{2015} * 7 2015 7^{2015} = 1 4 2015 14^{2015} . 1 4 1 14^{1} = 14... 1 4 2 14^{2} = 19 6 . 1 4 o d d 14^{odd} ends in 4... 1 4 e v e n 14^{even} ends in 6. 2015 is odd. 4

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