Crusoe can make 5 units of food per day if he devotes all his time to food production. He can make 10 units of clothing if he spends the whole day at clothing production. If he divides his time between the two activities, his output of each good will be proportional to the time spent on each. The corresponding figures for Friday are 10 units of food and 15 units of clothing. Describe the production possibilities frontier for their economy.