Three single rooms. Then the number is 47, distributed between 2 and 3 people. Among them, 3 rooms have the lowest price.

Then you can have 3* (triple room) +28 (double room) +3=50.

If the price of a triple room is the lowest, then the maximum number of triple rooms should be 47/3= 15.

It can be calculated that there are two people in a double room and 45 people in a 15 triple room, plus three single rooms.

Then the lowest total price is 3× 50+2× 30+45× 20 =150+60+900 =110 yuan.