A train travels 360 kilometers. 90 kilometers per hour, 4 hours; It takes more than four hours to drive 80 kilometers per hour. (search by positive and negative ratio)

Inverse ratio:

Solution: suppose it takes x hours.

90 * 4 = 80 times

80x=360

x=4.5

Positive proportion:

Solution: suppose it takes x hours.

90:80=x:4

80x=360

x=4.5