Promotional pricing shifts supply for petrol and demand for goods

Steps:

• Lower petrol price below competitors increases quantity supplied at that price, shifting petrol supply curve right.
• More customers buy petrol and enter store, boosting demand for groceries, shifting goods demand curve right.
• Petrol diagram shows lower equilibrium price and higher quantity.
• Goods diagram shows higher equilibrium price and quantity, increasing store revenue.

Why D is correct:

• Rightward supply shift for petrol follows supply-demand equilibrium, lowering price to attract buyers; rightward demand shift for goods reflects cross-product complementarity, raising sales.

Why the others are wrong:

• A: Left shifts reduce quantities for both, contradicting attraction strategy.
• B: Demand left for goods decreases store sales, opposite of success.
• C: Supply left raises petrol price, deterring customers.

Final answer: D