I'm afriad oldtimer is right despite his advancing age.
Your interest at the end of 75 days would be 10000*5.5%*75/365, so about €113.
Always look at the AER. It's the easiest way to compare deals. It's effectively the return you would get if you invested the sum for a year, i.e. every 75 days you got back your 10,000 + interest and reinvested the lot at the same rate for a year