A fort has enough food for 180 soldiers for 60 days. After 20 days, 60 soldiers leave. For how many more days will the remaining food last

Question: A fort has enough food for 180 soldiers for 60 days. After 20 days, 60 soldiers leave. For how many more days will the remaining food last-

Solution:
After 20 days: 180 soldiers had food for 40 days. Suppose 120 soldiers had food for x days.
Now, fewer soldiers, more days (Indirect Proportion):
120 : 180 : : 40 : x
⇒ 120/180 = 40/x
⇒ 120x = 180 × 40
⇒ x = (180 × 40)/120
∴ x = 60