Answer:
The number of kata that are taught varies from style to style. My style has 18 kata you have to learn before black-belt testing. There are several others that can be learned after one becomes a black belt.
the number of katas vary depending on which karate school you go to my school has 27 karate katas that you have to learn before you go to a black belt grading. there are a further 49 that you have to learn before you continue after black belt. some of them are made up by a number of instructors that belong to the same school and they make the kata specially for there school. there are also other kata that are known and used worldwide.