Take a look at the picture on the right. How much does one box of popcorn cost?
The correct answer, for this particular box, is $1.50. However it is not obvious that "two for $3" implies "one for $1.50". In other contexts, customers must make a minimum purchase to obtain a lower per-unit price. For example, if a shoe store has a "buy one pair, get a second pair free" sale, the customer who buys just one pair of shoes pays full price.
The actual per unit price of popcorn is not stated anywhere on the sign. Regular readers may recall a question from a financial literacy test used in a recent Statistics Canada Survey: True or false: By using unit pricing at the grocery store, you can easily compare the cost of any brand and any package size. In this case, the answer is false. The only unit price listed on the sign, 70.6 cents per 100 grams, corresponds to a price of $1.99 per 282 gram box, not the actual price of $1.50 per box.