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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.
Сalculate how many years ago the father was twice as old as his son.
(or in how many years he will be twice as old).
While he has not been 60 yet, he will be in 5 years.