Simplify the following text for a Grade 13 native English-speaking person.
Original: Not all manors contained all three kinds of land : typically , demesne accounted for roughly a third of the arable area , and villein holdings rather more ; but some manors consisted solely of demesne , others solely of peasant holdings .
Simplified: Not all manors had all three kinds of land : as an average , demesne accounted for roughly a third of the arable area and villein holdings rather more ; but some manors consisted solely of demesne , others solely of peasant holdings .