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http://codepen.io/t73biz/pen/gaZZgJ
Based off this image: images/calc.jpg
Objective: Build a CodePen.io app that successfully reverse-engineers this: http://codepen.io/GeoffStorbeck/full/zxgaqw.
Rule #1: Don't look at the example project's code on CodePen. Figure it out for yourself.
Rule #2: You may use whichever libraries or APIs you need.
Rule #3: Reverse engineer the example project's functionality, and also feel free to personalize it.
Here are the user stories you must enable, and optional bonus user stories:
User Story: As a user, I can add, subtract, multiply and divide two numbers.
Bonus User Story: I can clear the input field with a clear button.
Bonus User Story: I can keep chaining mathematical operations together until I hit the equal button, and the calculator will tell me the correct output.