Final answer:
An increase in the price of new guitars leads to a decrease in the quantity demanded. This is due to the downward-sloping demand curve that shows a negative relationship between price and quantity demanded.
Step-by-step explanation:
When the price of new guitars increases, the quantity demanded will decrease according to the law of demand. This does not mean that the demand will change; rather, the quantity demanded at the new, higher price is lower. This is a movement along the same demand curve, which slopes downward, indicating a negative relationship between price and quantity demanded. Demand curves for products like guitars typically slope down from left to right, illustrating that as price rises, quantity demanded falls. Therefore, the correct answer to the question is that, if the price of new guitars increases, quantity demanded will decrease, not the demand itself.