A farmer has peas and beans to sell at the market, but he only has one sack to transport them in. He comes up with an ingenious way to put both commodities into his one sack. The peas never touch the beans; they only touch the sack.

At the market he can dispense peas or beans independently from the sack; he pours the peas or beans directly from his sack into the customer's sack without allowing the commodities to touch any other surface or to touch each other. The sack doesn't have multiple compartments or multiple openings. This is all he has: an ordinary sack (which he can't cut or sew), some string (which he can cut), a supply of peas, and a supply of beans. Show how he could prepare his produce for transport to the market.