Please don't just tell us to get a better handle on cockpit workload management - there are times when I can't do the simplest of calculations, and dealing with an over-precise read-back would just overload my poor brain.
...you better learn to say "standby" more often then. An improper readback has the potential to kill you, just as much as getting those simple calculations wrong, perhaps more so. Prioritise, fine; but you cannot neglect such a safety critical task becasue you consider yourself a bit busy!