2000 sodiers in a fort had enough food for 20 days. But some soldiers were transferred to another fort and the food lasted for 25 days. How many soldiers were transferred?

Let the number of soldiers transferred be N
Now, the food would last for 25 days for (2000 - N) soldiers.
Less men, More days (indirect proportion)
25 : 20 : : 2000 : (2000 - N)
⇒ 2000 - N = (2000 x 20)/25
⇒ 2000 - N = 1600
∴ N = 2000 - 1600 = 400