4. (12 points) The magic school has received many magic balls, with a total weight of 5 tons. Each magic ball weighs 4 kilograms. Now, 10 students are using magic to color these magic balls. Each student can color 5 balls every 6 minutes. How many minutes will it take for them to color all the magic balls at the minimum?


【Solution】Solution: 5 tons $=5000$ kilograms, then the number of magic balls $=5000 \div 4=1250$ (balls). One person can color 5 balls in 6 minutes, so 10 people can color 50 balls in 6 minutes.

The number of 6-minute intervals needed to color all the balls is: $1250 \div 50=25$ (intervals).
The total time required to color all the balls is: $6 \times 25=150$ (minutes).
Therefore, the answer is 150.