Venn Diagrams and Negative Numbers I am confused about creating a Venn diagram from the question below from one of the past papers as there is a negative number involved. Is this possible in Venn diagrams?
A survey of students in a lecture revealed that a total of $15$ played rugby, $30$ played football and $35$ played cricket. $4$ people played all three sports, while $2$ played only football and rugby, $14$ played only cricket and football, and $6$ played only cricket and rugby.
If $4$ people played all three sports and $2$ played only football and rugby, how is it possible to create the Venn diagram? Are negative numbers allowed, as $2-4= -2$? 

Draw three circles such that each intersects the other two for your diagram. You will see that $3$ played only rugby, $11$ played only cricket and $10$ played only football. Try to fill in numbers into the regions one by one.
