A 2.5-pound bag of rice costs $4.00. What is the price per ounce? (1 pound = 16 ounces)

Convert the weight to ounces: $2.5\cdot16=40$ ounces. The price per ounce is $\frac{4.00}{40}=0.10$ dollars, choice A. Choice D ($1.60) is the price per pound, $\frac{4.00}{2.5}$, which does not convert to ounces. Choice C ($0.25) divides $4 by $16$, which treats the bag as a single pound. Choice B ($0.16) is $\frac{4}{25}$, which misuses the weight. A unit price for ounces must divide by the total number of ounces in the bag, which is $40$.