Lesson objective: Use estimation strategies, such as front-end estimation, to determine reasonableness of responses in measurement problems.

This lesson helps to build procedural skill with front-end estimation. A tape diagram is used here because it supports students' understanding of word problems through illustrating number relationships. This work develops students' understanding that, in addition to rounding, we can use mental computation strategies to assess the reasonableness of responses. By using a variety of mental computation strategies, students can recognize different estimation strategies may result in different estimates. It is important for students to discuss different strategies so they understand there is no one "right" estimate, but some estimation strategies produce estimates closer to the actual answer.

Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they plan a solution pathway by making meaning of the problem and estimating a solution that makes sense. Students should relate and connect their work to previous lessons involving measurement conversions and writing equations. Students should be able to look at their estimates and actual solutions and justify their reasoning.

**Key vocabulary:**

- estimation
- front-end estimation
- reasonableness

**Special materials needed:**

- Smartboard, document camera, or overhead projector