Simplify the following text for a Grade 10 native English-speaking person.
Original: A century leap year in the Gregorian calendar is a year that is exactly divisible by 400 ( and , thus , as with every other leap year , qualifies for the intercalation of February 29 ) : other century years ( with number divisible by 100 but not by 400 ) are common years .
Simplified: In the Gregorian calendar , a century leap year is a year that is exactly divisible by 400 ( and qualifies for the adding of February 29 , like all other leap years ) .