Lesson objective: Add and subtract to solve liquid volume problems.

This lesson helps to build procedural skills with reading and labeling milliliters on a liter graduated cylinder. A vertical number line is used here because it supports reading a scale on a graduated cylinder. This work develops students' understanding that drawings and representations can help solve addition and subtraction liquid volume problems.

Students engage in Mathematical Practice 1 as they use the graduated cylinder and vertical number line to understand the story of the problem, the meaning of the question, and what operation to use to solve the problem. Students engage in Mathematical Practice 5 as they write number equations to show their representations.

**Key vocabulary:**

- capacity
- equation
- liters
- milliliters
- number line

**Special materials needed:**

- graduated milliliter cylinder
- real world examples of 2 liter, 1 liter, 500 ml, and 250 ml bottles
- vertical number line for demonstration- enlarge number line to display 25 milliliters and/or 10 milliliters.