The Bank Account Rollercoaster: Tracking Transactions & Temperature
Shared by A STEM Educator
Students will apply operations with integers and rational numbers — including addition, subtraction, and the additive inverse property — to solve multi-step real-world problems involving bank transactions and temperature changes, and justify why subtracting a negative is equivalent to adding a positive.
Lesson Overview
Students use a bank account and winter temperature context to explore operations with integers and rational numbers, building from additive inverses to multi-step signed-number problems. The 3-Act structure moves from a compelling real-world hook to formal proof of why subtracting a negative equals adding a positive.
Materials
- Paper
- Pencils
- Whiteboard and markers
Scaffolded Task Progression
On your whiteboard, draw 5 plus signs (+) in a row. Now draw 5 minus signs (−) below them. Pair each + with a −. What is the total value of all 10 symbols together? Now try: if you have +8 and −8 in your account on the same day, what is the net change? Write the equation and explain what happened.
Teacher note: Model this verbally — 'Imagine you earn 8 dollars babysitting, but you also owe 8 dollars to a friend. You pay them back immediately. What's your net gain?' This is a zero pair.
The account starts at 47 dollars. There are 4 pending transactions. Some are positive (deposits), some are negative (withdrawals or fees). Without knowing the exact amounts yet, record three estimates:
- Too Low: a balance that would definitely be lower than the real answer
- Too High: a balance that would definitely be higher
- Best Guess: your most reasonable prediction
Explain your reasoning in one sentence.
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