Which is greater 2 thirds or 4 sixths?

They are equivalent.

2/3 = 4/6

Reason if you cancel 4/6 down by '2' you answer is 2/3 . Or conversely if you multiply 2/3 by '2' then you arrive at 4/6

'The symbol ' = ' means 'equivolence' , which means in mathematics, that the term is the same size (equal), but your are using different numerical values.