Episode of the week- Cellphone Repair

Purpose of this episode

Use percentages in a natural and relevant setting. Solve a mix of problems that require finding the part, the percentage, or the whole.


Noova needs a new cell phone! In this episode, children apply their understanding of percentages to help Noova choose the best deal.

Watch video walkthrough

Mathematical Background

Applying percentages effectively requires understanding the way in which the percentage is relative to the whole and how to use this as a basis for comparison and decision making. Children often struggle with the fact that percentages, unlike fractions in some contexts, are never absolute amounts and may find it hard to extract useful information from situations where they appear. Unlike previous episodes on the subject, such as On Sale, which offer interactive tools, here we “remove the scaffolding” - problems are presented as they would be in real life.

Furthermore, the problems in this episode give rise to advanced observations on percentages that go deeper into the relationships among the whole, the part, and the percentage.


What makes it great?

The questions are built to encourage insights within a setting relevant to children.

Who doesn’t want the best deal when shopping–especially for a new phone? Multiple strategies can lead to the correct answer, and the numbers have been carefully chosen to encourage critical thinking and help children gain problem solving skills.


Wrong answer sequences (WASes) provide useful visualizations.

Children have the freedom to fail and to learn from their mistakes. We provide effective and informative feedback that refers to the conceptual understanding of percentages developed in previous episodes.


Children are encouraged to follow their own journey.

The personalized feedback and hints help to reduce anxiety about this topic, impacting both the learning experience as well as children’s ability to apply their knowledge in the world. And like all of our episodes, children can replay the activity as they choose, seeing slightly different questions each time and allowing them to gain confidence in percentages.

Play it Yourself

Consonance with Our Pedagogical Principles