There is a board on the rollers. What happens to the board if two people run along it in the same direction? in opposite directions?

The board will move in the opposite direction; the board will be at rest if the product of speed and mass of one running person is equal to product of speed and mass of another.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.