How do I derive percentage in expression

Summary

How do I derive percentage in expression

Content

Hi 

We are looking to derive percentage for Joiner ratio by using two system fields : # Candidates Offered and # Candidates Hired.

And like to put expression like Hired/Offered * 100 but when I put it says invalid expression. 

Can anyone help how do I put an expression for achieve percentage. 

-Ranjeet

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