The purpose of this lesson is to put students' knowledge about addition and subtraction of signed numbers to use in real-life contexts. They work with tables that show the change, positive or negative, in quantities such as inventory or energy usage, and must make sense of these tables to answer questions about the context. An optional activity extends students' work with signed numbers on the number line to points in all four quadrants of the coordinate plane.
As students reason about quantities using signed numbers they engage in MP2.
- Apply addition and subtraction of signed numbers to solve problems in an unfamiliar context, and explain (orally and in writing) the solution method.
- Interpret signed numbers used to represent gains or losses in an unfamiliar context.
Let’s apply what we know about signed numbers to different situations.
- I can solve problems that involve adding and subtracting rational numbers.
When you put money into an account, it is called a deposit.
For example, a person added \$60 to their bank account. Before the deposit, they had \$435. After the deposit, they had \$495, because \(435+60=495\).
When you take money out of an account, it is called a withdrawal.
For example, a person removed \$25 from their bank account. Before the withdrawal, they had \$350. After the withdrawal, they had \$325, because \(350-25=325\).