While linus was waiting for the great pumpkin, he noticed some bats flying overhead. he found two bats could see out of the right eye three could see out of there left eye. four could not see out of the left eye, and 5 could not see out of the right. what is the least number of bats that linus saw that night and what might their eyesight have been?

Lets suppose,
R is right eye sighted only (left eye blind) 
L is left eye sighted only (right eye blind) 
B is both eyes sighted 
N is no eyes sighted (blind) 

We can deduce the following equations based on what we've been given: 
1) R+B=2 
2) L+B=3 
3) N+R=4 
4) N+L=5 

subtract equation 1 from equation 2 
L-R=1 

The smallest number we can start with is 1. 
Let's assume that R=1, and determine the other values based on this assumption. 
1) B=1 
2) N=3 
3) R=1 
4) L=2 

So we can calculate that Linus saw 7 total bats that night.  and they might have been 4 blind, 2 full sighted and 1 blind in the right eye only