When the demand for a commodity increases while supply remains unchanged, the equilibrium price and quantity will

Step 1: Analyze the question Demand increases, supply stays the same. We need to find what happens to both equilibrium price and equilibrium quantity.

Step 2: The concept Equilibrium is where the demand curve meets the supply curve. If demand increases, the demand curve shifts to the right (D₁ → D₂). The supply curve does not move.

Step 3: Working

• At the old equilibrium price, quantity demanded now exceeds quantity supplied, so there is a shortage (excess demand).
• Buyers compete for the limited goods, which pushes the price up.
• As price rises, suppliers are encouraged to produce more. This is a movement along the supply curve (an extension in supply), not a shift.
• A new equilibrium forms at a higher price and a higher quantity.

Example: Suppose the equilibrium is ₦100 with 50 units. Demand rises, and the new equilibrium becomes ₦120 with 60 units. Both price and quantity have increased.

Step 4: Check the options

• A. Increase: correct, both price and quantity rise.
• B. Remain constant: wrong, a demand shift changes the equilibrium.
• C. Decrease: this would happen if demand fell.
• D. Turn negative: price and quantity cannot be negative in this context.

Tip: Remember the rule for a single shift with the other curve fixed:

• Demand ↑ → price ↑, quantity ↑
• Demand ↓ → price ↓, quantity ↓
• Supply ↑ → price ↓, quantity ↑
• Supply ↓ → price ↑, quantity ↓

Demand moves price and quantity in the same direction, while supply moves them in opposite directions. This pattern comes up often in WASSCE, JAMB and NECO.