Description for Correct answer:
Let the number of soldiers transferred be x.

Now, the food would last for 25 days for \( \Large \left(2000 - x\right) \) soldiers.

Less men, More days (Indirect proportion)

25 : 20 :: 2000 : 22000-x

= 2000 - x = \( \Large \frac{2000 \times 20}{25} \)

= 2000 - x = 1600

Therefore, x = 2000 - 1600 = 400