Citizen Math used to be called Mathalicious. If you have a current account on Mathalicious, you can use those credentials to log in to your Citizen Math account. Learn more here.

# Datelines

## How much does age matter in a relationship?

How much does age matter in a relationship? While some people believe that love knows no bounds, others think that partners should still be relatively close to one another age-wise.

In this lesson, students use a system of linear inequalities to explore the popular dating rule-of-thumb, ‘half plus seven’, and debate how important age -- and other factors -- are in healthy relationships.

### REAL WORLD TAKEAWAYS

• In a relationship it’s important to be able to relate to the other person – to have common experiences and shared priorities and mutual interests. Age is one factor that might contribute to or hinder this, but it’s certainly not the only one.

### MATH OBJECTIVES

• Write linear inequalities from a verbal description
• Graph a system of linear inequalities with a domain restriction
• Write and solve inequalities to answer real-world questions
• Find an inverse function

Appropriate most times as students are developing conceptual understanding.
Algebra 1
Solving Linear Systems
Algebra 1
Solving Linear Systems
Content Standards A.CED.2 Create equations in two or more variables to represent relationships between quantities; graph equations on coordinate axes with labels and scales. A.REI.12 Graph the solutions to a linear inequality in two variables as a half- plane (excluding the boundary in the case of a strict inequality), and graph the solution set to a system of linear inequalities in two variables as the intersection of the corresponding half-planes. F.IF.5 Relate the domain of a function to its graph and, where applicable, to the quantitative relationship it describes. For example, if the function h(n) gives the number of person-hours it takes to assemble n engines in a factory, then the positive integers would be an appropriate domain for the function. F.BF.4 Find inverse functions. (a) Solve an equation of the form f(x) = c for a simple function f that has an inverse and write an expression for the inverse. For example, f(x) =2 x<sup>3</sup> or f(x) = (x + 1)/(x &mdash; 1) for x = &dash;1. (b) (+) Verify by composition that one function is the inverse of another. (c) (+) Read values of an inverse function from a graph or a table, given that the function has an inverse. (d) (+) Produce an invertible function from a non-invertible function by restricting the domain.
Mathematical Practices MP.4 Model with mathematics. MP.5 Use appropriate tools strategically.