In a week, Cindy spends an average of 48 hours/week / 4 courses = 12 hours/week for 1 math course.
In a month, 1 math course is 12 hours/week x 4 weeks/month = <<12*4=48>>48 hours.
Therefore, she earns $25/hour x 48 hours/week = $<<25*48=1200>>1200 a month for 1 math course.
#### 1,200