Quantity of cheerios cereal in the smaller box Hannaford sold = 9 ounces
Cost of nine ounces of cheerios cereal = $2.50
Cost of one ounce of cheerios cereal :


Cost of one ounce of cheerios cereal in the smaller box = $0.27
Quantity of cheerios cereal in the larger box Hannaford sold = 20 ounces
Cost of nine ounces of cheerios cereal = $3.79
Cost of one ounce of cheerios cereal :


Cost of one ounce of cheerios cereal in the larger box = $0.18
Difference in their cost per ounce :


Therefore, the difference in cost in dollars per ounce between the two sizes = $0.09