Lesson objective: Extend understanding that addition, subtraction, multiplication, and division can be used to solve multi-step measurement problems.

Students bring prior knowledge of solving addition, subtraction, multiplication, and division measurement problems from 3.MD.A.1 and 3.MD.A.2. This prior knowledge is extended to multi-step problems as students develop deeper mathematical thinking and become stronger problem-solvers. A conceptual challenge students may encounter is deciding which operation(s) a word problem requires.

The concept is developed through work with bar diagrams and number lines, which provide a visual representation of the given information, and can be used to write an equation and make sense of the problem. Through the use of the bar diagram and written equation, students are more likely to choose the appropriate strategy to solve the problem.

This work helps students deepen their understanding of operations because students need to be able to connect the emphasis on the operation involved to the word problem, not the key word or words. Through strong understanding of the operation or operations involved in word problems, students are better able to visualize and write equations to make sense of the problem.

Students engage in Mathematical Practice 1 (make sense of problems and persevere in solving them) as they understand different approaches to problem solving. Students should seek first to understand the problem, then solve it. Students should encounter road-blocks and be able to communicate with others how they overcame obstacles on their path to problem-solving.

**Key vocabulary:**

- elapsed time
- intervals
- measurement

**Special materials needed:**

- clock