The original number of students in the hostel was 50, and now it is 80 because 30 joined. So the original number of students was 5/8 of what it is now.
I use the inverse formula the number of days the food will last.
40 * 5/8 = 200/8 = 25
If there are 80 students, then the food will only last for 25 days.
