If the old man walks 2/3 of a mile in 1/2 an hour, you can find how many miles he walk in one hour by setting up a fraction where distance (miles) is the numerator and the denominator is time (hours). So, (2/3)/(1/2) is the fraction. Now, we have to figure out how to make the denominator one, and we do that by multiplying is by 2. Whatever you do to the denominator you have to do to the numerator, so multiply 2/3 by 2 and 1/2 by 2.
(1/2) x 2 = 1 and (2/3) x 2 = 4/3 or 1 1/3
the old man walked 1 1/3 miles per hour