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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
I probably should have worded the error messages more clearly. By "Returned string", it means your function returned a string instead of a number.
You must return a number, but toFixed() returns a string.
I've randomized the radii, provided better examples and improved the error messages. They should now tell you if you are submitting a string, NaN, etc.