Of which

English as a Second Language English Vocabulary, Grammar and Idioms
1

Which one is correct? What is the definition of “of which” and how do we use it?

There are 100 staff, of which one-third is female
There are 100 staff, of which one-third of them is female

Thanks

2

Only the first is correct. ‘Of which’ = of them. The second verb should be ‘are’.