5,10-2,3

Likely interpretation: you’re using a decimal comma.

Compute: 5,10 − 2,3 = 5,10 − 2,30 = 2,80

So the result is 2,80 (which is 2.8 in decimal with dot, or 14/5 as a fraction).

Would you like it in a different format (2.8, or 14/5), or is there another operation you meant?