Simplify the following text for a Grade 7 native English-speaking person.
Original: Groupings are based on different sales benchmarks , the highest being for claims of at least 50 million copies , and the lowest being for claims of 20 â `` 29 million copies .
Simplified: Groupings are based on different sales benchmarks . The highest benchmark is for claims of at least 100 million copies , and the lowest are for claims of 20 â `` 29 million copies .