Lisa surveyed 60 students at her school and found that 0.85 of the students she surveyed said their favorite class is math. another 15% of the students she surveyed reported that their favorite class is science. how many more students in the survey prefer math over science?

First I would convert the .85 into an 85%

Now you have 85% like math and 15% like science.

Since there are 60 students, you then take .85*60=51 students who prefer math and .15*60=9 students who prefer science. 

Then you take math (51) minus science (9) 

51-9=42 more students prefer math over science