8*7=56

60-56=4

4÷( 15-7)= 1/2

60- 15× 1/2=52.5

5× 1/2=5/2=2.5

52.5+2.5=55

55÷5= 1 1

Need 1 1 cow.

2、 10×20=200 15× 10= 150

200- 150=50 50÷(20- 10)=5

200- 5×20= 100

25-5=20

100÷20=5

If 25 ticket gates are opened at the same time, the queue disappears after 5 minutes.