A motorcyclist went from Michigan to Ohio at a speed of 90 mph. On the way from Ohio to Michigan his speed was 120 mph. The time of the second trip was 1 hour less than it was the first time. What was the time of the trip from Michigan to Ohio?
Let's denote the time of the trip from Michigan to Ohio as t.
The time of the trip from Ohio to Michigan is t - 1.
We know that distance equals speed multiplied by time, so the distance of both trips is the same.
Thus, the speed multiplied by the time for the trip from Michigan to Ohio gives the same distance as the speed multiplied by the time for the trip from Ohio to Michigan.
So, 90 mph * t = 120 mph * (t - 1).
Multiplying through parentheses gives 90t = 120t - 120.
Subtracting 90t from both sides gives -30t = -120.
Dividing both sides by -30 gives t = 4.
Therefore, the time of the trip from Michigan to Ohio is 4 hours. Answer: \boxed{4}.