Lesson objective: Understand that estimation and place value can be used to determine reasonable products

Students bring prior knowledge of multiplication from 4.NBT.B.5. This prior knowledge is extended to determining reasonableness as students use estimation to predict a reasonable product using the standard algorithm. A conceptual challenge students may encounter is thinking that digit values are not important when calculating using the standard algorithm, or that you simply multiply digits and not their values.

The concept is developed through work with estimating the product of numbers in a real world scenario to determine if an answer is reasonable.

This work helps students deepen their number sense and understanding of place value and its role in the standard algorithm because multiplying digit values is essential to successful use of the standard algorithm.

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they continue to use the standard algorithm and determine the reasonableness of their results. Students should recognize when digit values have not been multiplied correctly and when the algorithm has been applied incorrectly.

**Key vocabulary:**

- algorithm
- digit value
- estimation
- multiplication
- place value
- product
- standard algorithm