(1) If 9t fresh milk is made into yogurt, the profit is 1200× 9 = 10800 yuan.
(2) If all milk powder is produced within 4 days, 5t fresh milk will be wasted without processing, and the profit is only 2000× 4 = 8000 yuan.
(3)4 days, it takes X days to produce yogurt and 4-X days to produce milk powder, and it is guaranteed to process 9t fresh milk as scheduled.
From the meaning of the title, 3x+(4-x) × 1 = 9. The solution is x = 2.5.
Therefore, 4-x = 1.5 (days). So for 4 days, if yogurt is produced in 2.5 days and milk powder is produced in 1.5 days, the profit is (2.5 * 3 *1200+1.5 *1* 2000.
Answer: Organizing production according to the third scheme can make the factory gain the most, and the maximum profit is 12000 yuan.