Analysis: The fuse should be at least x cm long. Because it is necessary to move to a safe area 400 meters away before blasting, the burning speed of the fuse is 1.2cm/ s, and the speed of people leaving is 5 m/s. According to the same time, the equation 400/5 > x/ 1.2 can be listed and solved.

Solution: Solution: Set the fuse to be at least x cm long.

According to the meaning of the question

400/5>x/ 1.2，

X > 200/3，

Answer: The fuse should be at least 200/3cm long/