Farmer's Sheep
Answer :

The farmer had one sheep only! 

If he divided this sheep (which is best done by weight) into two parts, making one part two-thirds and the other part one-third, then the difference between these two numbers is the same as the difference between their squares—that is, one-third. 
Any two fractions will do if the denominator equals the sum of the two numerators.. 

Math Genius