Students will engage in many problem situations as they develop algorithms for adding, subtracting, multiplying, and dividing decimals. They will explore percents in the context of tip, tax, discount, and total cost. Students have two ways of making sense of what decimals mean—extending the place-value system on which our number system is built or interpreting decimals as fractions. In order to have the most complete understanding of and skill with computation, students need to understand each of these meanings. Then they use them to examine why decimal algorithms for addition, subtraction, multiplication, and division make sense. Depending on the operation, the fraction interpretation or the place value interpretation may help in finding short-cut algorithms.