arithmetic - a military camp has a food reserve for 250 person for 40 days if after 10 days 50 more person are added to the camp find the number of days the reserve will last for - skillgun

As the camp has a reserve for 250 person that can last for 40 days, after 10 days the reserve left for 250 person is for 30 days. Now 50 more person are added in the camp.
Hence, the food reserve for 300 person will last for:
250:300::x:30 ……..(it is an indirect proportion as less men means more days)
x = (250*30)/300
x = 25 days