According to the meaning of the question, 1/3 days later, the owner began to chase after riding a horse, and it was already 3/4 of the day when the owner got home.

Explain that it took the host (3/4- 1/3 )/2=5/24 days to catch up with the guests, and the time to catch up was.

1/3+5/24= 13/24 days.

That is to say, the distance traveled by the owner's horse in 5/24 days is equal to the distance traveled by the guest's horse 13/24 days, and this distance =300* 13/24.

Then the speed of the master horse is 300 * 13/24/(5/24)= 780km/ day.