Final answer:
The minimum safe following distance when driving 40 mph in packed snow is around 16 to 20 meters, which is equivalent to 4 car lengths.
Step-by-step explanation:
The minimum safe following distance when driving 40 mph in packed snow depends on reaction time, road conditions, and the rate at which the car can stop. Generally, it is recommended to leave a following distance of at least 4 car lengths.
One car length is typically considered to be around 4 to 5 meters. So, 4 car lengths would be about 16 to 20 meters.
It is vital to maintain a safe following distance to allow for proper reaction time and to avoid collisions, especially in treacherous road conditions.