Quickly read the question and the answer choices to get a feel for what the question is specifically asking. Translate the equation to paper and translate the question into an expression with variables. If a percentage is given, move the decimal two places to the left to express its equivalent decimal form. Since the retail price is not given, the percentage markup that we seek must be the same for all trade books. Let P be the original price.
Solution Let R be the number of residents.
Solution Let x be the gallons of pure water to be added. The amount of salt will remain constant.