Perry surveyed 60 students at her school and found that 0.45 of the students she surveyed said their favorite class is math. Another 35% of the students she surveyed reported that their favorite class is science. How many more students in the survey prefer math over science?
In the survey, 60 x 0.45 = <<60*0.45=27>>27 students prefer math.
And 60 x 35/100 = <<60*35/100=21>>21 students prefer science.
Thus, 27 - 21 = <<27-21=6>>6 more students prefer math over science. Answer: \boxed{6}.