Lesson objective: Apply knowledge of adding and subtracting decimal numbers.

This lesson provides an opportunity for students to apply their knowledge and understanding of adding and subtracting decimal numbers to a real-life situation. Students are asked to work out how many items Helen can put in the box without going over a weight limit of 5 lbs.

Key Concept students will use:

- The meanings of addition and subtraction are the same when used with decimals as when used with whole numbers.

Skills students will use:

- adding and subtracting decimal numbers

Students engage in Mathematical Practice 2 (Reason abstractly and quantitatively). Students are able to decontextualize real world situations such as comparing packaging items without exceeding a weight limit and transform them into symbolic representations in a subtraction or addition problem.

**Key vocabulary: **

- place value
- decomposing
- units of value
- decimal point

**Special materials needed:**

- Squared paper could be useful if students struggle to keep their digits aligned by place value.