Those in favour:
=(Quantity Yr11 Students)(0.75) + (Quantity of Yr12 Students)(0.60)
=(320)(0.75) + (280)(0.60)
=408 students
Probablity of a Year 11 Student:
=(Quantity of Yr11 Students)(0.75)/(Total Students)
=(240)/(600)
=0.4 = 40%
Percentage:
=(Students in favour)/(Total Students)
=408/600
=0.68 = 68%