With people settling down, starting a family, and even dying later and later, it’s becoming a common refrain that “30 is the new 20.” But what does this mean, and how might your life change if your life expectancy were different?

In this lesson, students use proportions to determine what life expectancy must have been in order for 30 to really be the new 20. They then extend their proportional reasoning to calculate the age at which certain life events would’ve happened in the past. Finally, they explore what might happen in the future, in a world where life expectancy hits 200 years.

### Students will

• Come up with a proportional definition of the phrase “30 is the new 20”
• Use a shorter life expectancy to calculate the age at which life events may have happened in the past
• Use a longer life expectancy to calculate the age at which life events may happen in the future
• Discuss whether or not life events really happen at ages proportional to life expectancy

### Before you begin

This lesson focuses heavily on proportional reasoning, so it’s best if students have been exposed to proportions before (though mastery of proportions isn’t assumed). One question involves a line graph, so it will help if students have seen these types of graphs before, but previous experience isn’t necessary.