A fort had food provisions for 150 men for 45 days. After 10 days, 25 men left. How many days will the remaining food last?

To find how long the food lasts after 25 men leave, calculate the total food supply in man-days and divide by the remaining men. Step 1: Initial provision = 150 men × 45 days = 6750 man-days. Step 2: Food consumed in 10 days = 150 men × 10 days = 1500 man-days. Remaining food = 6750 - 1500 = 5250 man-days. Step 3: Remaining men = 150 - 25 = 125. Days left = 5250 / 125 = 42 days. Verify: 125 × 42 = 5250 man-days, matching the remaining food. Options A, C, and D are incorrect. Thus, the correct answer is B.