Grammar for the IELTS writing task 1

Please let me know if these sentences were grammatically right, and show me how to do it properly if possible. Thanks in advance.

-There was a higher proportion of part-time workers among graduates compare to postgraduates.

-There was a higher proportion of part-time workers among graduates than postgraduates.

-The proportion of those who did part-time work in graduate students is higher than that of postgraduates

-The proportion of those who did part-time work in graduate students is higher than postgraduates