formula to determine how many rows have different values in two columns (mismatches)

Is there any formula that I can put in a different sheet that counts how many rows of data on another sheet have different values (mismatches) on two columns?
For instance in the below example, the answer is 2:

25 25
46 46
73 28
56 56
80 80
47 36

Please note that there are also blank rows. I would also like to have the summary of net unmatched provided that on a thrid column there is a particular reference. For example in the above range if all rows have that reference, the answer would be 73-28 + 47-36 = 56

Thanks in advance,

It works! Thanks a lot.