What would have been our number system if humans had more than 10 fingers? Try to solve this puzzle. Try to solve this puzzle:

The first expedition to Mars found only the ruins of a civilization.
  From the artifacts and pictures, the explorers deduced that the
  creatures who produced this civilization were four-legged beings with
  a tentatcle that branched out at the end with a number of grasping
  "fingers". After much study, the explorers were able to translate
  Martian mathematics. They found the following equation:
  $$5x^2 - 50x + 125 = 0$$
  with the indicated solutions $x=5$ and $x=8$. The value $x=5$ seemed
  legitimate enough, but $x=8$ required some explanation. Then the explorers 
  reflected on the way in which Earth's number system developed, and found
  evidence that the Martian system had a similar history. How many fingers would 
  you say the Martians had?
$(a)\;10$
$(b)\;13$
$(c)\;40$
$(d)\;25$

P.S. This is not a home work. It's a question asked in an interview.

Historically we kept using different number systems much later than we had 10 fingers. We have an innate ability of recognizing up to 3-5 items without any counting takes place. It is called subitizing. Some animals exhibit the same behavior too. So it's not about the fingers but about recognizing digits at one look. Base ten is great for that.
Fingers are extensions that are subject to functionality/resources trade-off just like branches or caterpillar feet. Especially a ridiculously complex move such as grasping requires precision hence lots of extra muscles and nerve complications. Think of all the animals that can and cannot grasp. You'll see a pattern. 
Without delving into any mathematics I would say object to the question that it is very unlikely to have that many fingers for grasp capable tentacle (it says the history is similar). 
So offer the game instead of the piece. 
