Is it possible to sort based on an arthimatic operation in Ruby on rails active record?

I want to order records based on two columns Arthimatic operation.

Ex: I has two columns on which I has to do an arthimatic operation and sort based on its value. Let the two fields be math, science and total.And table name is UserMark. Typically my query looks like this

UserMark.order('(math/total) desc')

This should order the UserMarks based on math/total operation.How could it be done in Ruby on rails?