The purpose of this activity is to use multiplication and division to solve area problems. In most cases, the area and one side length are given and students can use division to find the unknown side length. In one case, the two side lengths are given and students find their product, which is the area.

• Ask selected students to share their work and explain their steps.
• “How can we make sure that we found the correct missing side lengths?” (Multiply the length and the width together to make sure it gives the area, or divide the area by one of the side lengths and make sure it gives the other side length.)
• “How was finding the area of the rectangle, using the length and the width, different than finding one of the side lengths, using the area and the other side length?” (I had to multiply to find the area from the length and the width. I used division to get one side length from the area and the other side length.)

The purpose of this activity is for students to apply what they learned about dividing multi-digit numbers to find the unknown side length(s) of rectangular prisms, given the volume and at least one other side length. As in the previous activity, both multiplication and division are important to solve the problems. This is true both because finding partial quotients uses multiplication and because they have different choices for how to find an unknown side length when two side lengths and the volume are given. Monitor for students who:

• Find the product of the two given side lengths and then use division to find the third side length. 
• Divide successively by the two given side lengths.

• Ask students to share their work and their reasoning.
• Highlight multiple approaches to find the unknown side lengths in the second and third tables.
• Display the second row of the third table.
• “What are some different ways you can find the length of this rectangular prism?” (I can first divide the volume by 2 and then divide by 48, or I can multiply 2 and 48 and then divide the volume by that product.)
• “Which method did you prefer? Why?” (I divided the volume by 2 and then by 48 because that was quick and kept the numbers smaller.)