Question: There are enough provisions in a castle to feed 300 people for 90 days. After 30 days, 100 people leave the castle. How many more days are left until all the food runs out? Think carefully first, then make a decision:
After 30 days, there will be enough food left to sustain 300 people for 90 days 30 days = 60 days. After the 100 people leave, there will be 300 - 100 = 200 people left. The 200 people will eat 200 / 300 = 2 / 3 as much food as the original group of people in the castle. The 60 days' worth of food will last this smaller group for 60 days / (2 / 3) = 90 more days. So the answer is 90.