The difference between 21 and 17 is: 
The difference between 65 and 61 is: 
The difference between 28 and 17 is: 
The difference between 21 and 10 is: 
The difference between 51 and 17 is: 
The difference between 21 and 17 is: 
The difference between 25 and 11 is: 
The difference between 21 and 17 is: 