There's a fine line between numerator and denominator. Only a fraction will find this funny. It's quite divisive!
This joke talks about the literal line between a numerator and denominator, called a "vinculum" and compares it to the saying "there's a fine line between x and y". It also refers to fractions being related to a form of division, making it quite divisive!
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Three statisticians go duck hunting. They see a duck and the first statistician shoots, hitting two feet to the left of the duck. The second statistician shoots, hitting two feet to the right of the duck. The third statistician leaps up in joy, yelling, "We got it!"
This is an average joke. And by that, I mean that the joke is referring to the average (the middle point) of the first and second statisticians' shots. If you go exactly between a shot that is two feet to the left and a shot that is two feet to the right of a duck, you would find the duck right in the middle! This is why the third statistician expresses joy that the duck has been hit. The duck hunt in this scene comes from the 1984 video game by the same name. 

Not everyone understands the mathematician's team spirit
The mathematician's sign proudly states: "Our team is #0!" Those that know 0! (read zero factorial) is equal to 1 will think the mathematician is a great supporter of the team. However, others could definitely read it as "Our team is number zero!" Definitely not as supportive as the mathematician intended. 

Math, the only subject that counts 
Now before you get offended (or start bragging), the "counts" here refers to the action of counting generally given over to the realm of math.