Divide the miles he traveled by the time it took him to travel it.
22 1/2 / 1/3
Multiply by the reciprocal of 1/3:
22 1/2 * 3/1
Convert 22 1/2 into an improper fraction:
45/2 * 3/1
Multiply the numerators and denominators together:
135/2
Divide:
67.5 or 67 1/2
So his average speed in miles per hour is 67 1/2.