In this rather different lesson, I'd like to cover a fun topic on how to utilize the power of Math to make your application behave the way you want. The application we'll build out today is the number pad on the phone app for your iOS devices. To lay out everything correctly, I'll show you how to calculate the sizes of each key based on the entire width of the screen. This way, when you load your app onto an iPhone 5s, you can have the same size ratio for your elements. Enjoy.