Description: In Lesson 19, students initially use the place value chart to multiply by multiples of 10. They see that when multiplied by 10, the digits in the product shift one place value to the left. Complexities are addressed as regrouping becomes involved with problems like 4 × 6, where the product has mixed units of tens and ones. However, the same principle applies-the digits shift once to the left. Lesson 20 carries students' understanding from Lesson 19 to more abstract situations using a wider range of multiples of 10. Students learn to model place value strategies using the associative property. In Lesson 21, students apply learning from Topic F to solving two-step word problems and multiplying single-digit factors and multiples of 10. They use the rounding skills learned in Module 2 to estimate and assess the reasonableness of their solutions.