The difference between 81 and 81 is: 
The difference between 87 and 23 is: 
The difference between 88 and 81 is: 
The difference between 81 and 80 is: 
The difference between 91 and 81 is: 
The difference between 81 and 51 is: 
The difference between 80 and 81 is: 
The difference between 81 and 81 is: 