1 Calculate the percentage change in the price of a smoothie and the percentage change in the quantity demanded of smoothies. A rise in the price of a smoothie from £2 to £3 results in a fall in the quantity of smoothies demanded from 220 million to 180 million a day and at today’s price of a muffin, £1.50, the quantity of muffins demanded rises from 80 million to 100 million a day.