Checkley said yes, so let's find out for sure:

 

with , , 

 

 





 







Using the +,



Using a calculator:



That rounds off to 0.28, so you're right on that one.


Using the -,



Using a calculator:



That rounds off to -14.28.  Uh oh! You missed the
sign on that one. Checkley didn't notice.
But you were half right!

Edwin