If a housewife has meat and wants tomatoes, she must find someone who has tomatoes to give and wants meat. This concept is described as

Step 1: Analyze the question A housewife has meat and wants tomatoes. To get them, she must find someone who has tomatoes and wants meat. This describes a trade without money, where goods are exchanged directly for other goods.

Step 2: Explain the concept This is barter trade. Its main problem is the need for a double coincidence of wants. This means two people must each have what the other wants, at the same time, before a trade can happen. It is one of the key reasons money was introduced as a medium of exchange.

Step 3: Check each option

• A. Scale of preference: This is a list of a person's wants arranged in order of importance. It has nothing to do with finding a trading partner.
• B. Opportunity cost: This is the next best alternative given up when a choice is made. It does not apply here.
• C. Complementary demand: This is demand for goods used together, such as bread and butter, or cars and fuel. Meat and tomatoes are not being treated this way here.
• D. Double coincidence of wants: This fits exactly. She has meat and wants tomatoes, while the other person has tomatoes and wants meat.

Step 4: Answer The correct option is D. Double coincidence of wants.

Exam tip: Whenever you see "barter," "exchange without money," or "I have X and want Y, so I must find someone who has Y and wants X," think double coincidence of wants. It is a classic JAMB and WASSCE point about the weakness of barter and the need for money.