Worked problem part 1,2,3 a rise in the price of a smoothie from $2 to $3 results in a decrease 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 increases from 80 million to 100 million a day. 1. calculate the percentage change in the price of a smoothie and the percentage change in the quantity demanded of smoothies. hint: use the average price and average quantity to calculate the percentage changes. the price of a smoothie changes by 25 percent and the quantity demanded of smoothies changes by 10 percent.