Y= 0.75 X (given)
Let, Y= total no. of girls and X= total no. of Boys
80% of the total students passed the exam successfully; (X+Y)*0.8
And 90% of the girls passed the exam too; 0.9*Y
thus we can write, (X+Y)*0.8 = 0.9*Y + X* (percentage of the boys who passed the exam)
1.75*0.8*X = X( 0.9*0.75 + Percentage of the boys who passed the exam)
Percentage of the boys who passed the exam = 72.5%