When family members share a wireless plan, how should they split the bill? What if someone goes over the maximum allotted messages, voice minutes, or megabytes of data? And when should they change to a different plan?

In this lesson, students use proportional reasoning to predict whether a family will exceed their wireless plan allotment. They write and evaluate numerical expressions to decide how to split the bill fairly, and explain whether it makes sense to upgrade their plan.

### Students will

• Use proportional reasoning to predict 30 days of cell phone usage based on 1, 7, and 15 days
• Calculate the monthly bill for two siblings on a family plan, including flat-rate items and overages
• Based on his/her usage, determine how much each sibling should pay
• Evaluate alternative wireless plans, and decide whether up- or downgrading would better fit their wireless behavior and save them money in the future

### Before you begin

Students should be able to perform operations on decimals and apply the order of operations. The lesson applies unit rates and involves proportional reasoning, but extensive prior experience with these is not assumed. The focus in this lesson is more on constructing and communicating logical arguments than it is on sophisticated mathematics.