I have strep throat. i have some amoxicillin left over, amoxicillin 250 mg and amoxicllin-k clavulanate 875-125 mg. can i mix these for 10 days?

Are you asking if: you can take them together? Adding 250mg of amoxicillin to amoxicillin-clavulanate will NOT provide any additional benefit. Taking them sequentially doesn't make much sense either. If your strep test was (+), you do need the equivalent of a 10 day course of antibiotics. Plain amoxicillin 875 mg 2x/day for 10 days is a effective alternative to amox-clavulanate & has fewer side effects.