The ratio of boys and girls in a class is 4 : 5. If 10% of the boys and 20% of the girls failed in an examination, what percentage of students passed in the exam?

প্রশ্নঃ The ratio of boys and girls in a class is 4 : 5. If 10% of the boys and 20% of the girls failed in an examination, what percentage of students passed in the exam?