Solution: 120× 1/3= 40 sets sold on the first day.

40×5/8= 25 sets were sold the next day.

There are 120-40-25=55 sets left.

23. The speed ratio of the two trains A and B is 5:4. Train B starts first. When the distance from B to A is 72km, train A goes from A to B, and the distance ratio between the two trains and AB is 3:4. So how many kilometers are there from AB?

Solution: When we meet.

A walked 3/7 of the whole journey, so B walked 1-3/7=4/7 of the whole journey.

Because "the ratio of the distance between two trains and AB is 3:4"

Because the speed ratio of Party A and Party B is 5: 4 = 1: 4/5.

Then the distance ratio between Party A and Party B = 1: 4/5.

So line A is 3/7, and line B is 3/7×4/5= 12/35.

So the whole journey = 72/(4/7-12/35) = 72/(8/35) = 315 km.