Hi aspirant,

The question mentioned above can be easily solved by applying the concept of unitary method. If for 50 soldiers food is sufficient for 30 days, then for one soldier food will be sufficient for 50*30 days . Now if 25 more men are are included in the camp the total number of soldiers become 75. Therefore now the food will last for, 50*30/ 75 days which is equal to 20 days.

Hope it helps!!