How do I find Marginal Price (MP) and Average Price (AP)? This is for economics and I am looking at a table with values showing an increase in price per units depedning on how much water you consume. For example, from 0-999 gallons, it costs $0.5 per gallon. From 1000- 1999 gallons, it costs $.75 per gallon. So how do I calculate the MP and AP? Thanks!