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