Male students in the senior class = M
Female students in the senior class = F
Therefore,total students= M+F
Number of male students who applied for college = (72/100)M
Number of female students who applied for college = (80/100)F

Therefore total students who applied for college = (72/100)M + (80/100)F

From (2) it is given that a total of 75% students apllied for college i.e. (75/100)(M+F)

Therefore (75/100)(M+F) = (72/100)M + (80/100)F

Solve the above equation to get 5F = 3M
Therefore the ration of male students to the total no of students = M/(M+F)
i.e M/(M+(3M/5)) WHICH GIVES THE RATIO AS 5/8