1. The problem statement, all variables and given/known data Hello guys, I've attempted a problem but I get a result that I find too low to make sense. Plus, I have a doubt. So here it comes: I've put in red the part I'm unsure of. As far as I know the efficiency of a refrigerator could be any real number from 0 to infinity (1 is not the limit!). So what exactly is 15% of the "ideal" coefficient performance?! The ideal would be an efficiency of infinity?! 2. Relevant equations Not many. 3. The attempt at a solution Per day there are 750 kcal =3139.5 kJ entering the refrigerator. 1kW h =##3.6 \times 10^ 6 J## which corresponds to a price of 0.025$. So if by efficiency of 15% of the ideal one they mean that for each calory that enters the refrigerator I must pay as if I remove 1/0.15 =6.667 calories out of it, then I reach that I must pay as if I must remove 20930 kJ per day. This corresponds to approximately 0.145$ per day. So in a month, 4.36$ only. The result seems too low to me and I don't understand why they give the data of "2°C" nor exactly what they mean by 15% of the ideal coefficient performance. Thanks for any help.