Friday, 30 October 2015

elementary number theory - If p=1cdot3cdot5cdot7cdot9cdot...cdot2011, then the units digit of p is five



I know there is a 5 on the sequence, but i don't know how and why his presence leads to the final units digit of the product.



Answer



Hint: All odd numbers divisible by 5 end in 5.


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