1200 men has food provisions for 25 days.
So, number of men [ x ] = 1200 , 300
number of days [ y ] = 25 , y2
When there are more men, food provisions for them will be there for less days.
When there are less men, food provisions for them will be there for more days.
So, it is an inverse proportion.
So, x1y1 = x2y2
ie, 1200 * 25 = 300 * y2
So, y2 = 1200 * 25 / 300
= 30000 / 300
So, if there are 300 men, the food will last for 100 days.