Code challenge- Creating flexible margins. System glitch?

Hello everyone. I seem to be having alot of technical difficulty in a few code challenges. I am working on Building a responsive website. In a previous challenge, I was converting widths to percentages. The answers i was providing were showing up as wrong but based on the formula it was correct. A few days later i logged in and entered my same answers and then it took. Now i am faced with the same situation. In the section "Creating Fluid Foundation". The code challenge it is asking me "Using .icing as your context, convert the margins on .cake from pixels to percentages". Cakes margin is 10px and icings context is 500. based on the formula i have learned i did... Target divided by Context = Result. so 10px divided by 500=0.02 carry the decimal to places to the right and it =2% I wrote out my answer exactly as follows... Margin:2%; /10px / 500 =0.02/ I'm not understanding how this is incorrect and this is very frustrating. Is it another system glitch? Please help, It would be greatly appreciated.