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

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

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