The unitary method is a technique which is used for solving a problem by finding the value of single unit, i.e., 1, (by dividing) and then finding the necessary value by multiplication the single unit value. In essence, the unitary method is used to find the value of a unit from the value of a multiple (by dividing), and thence the value of a multiple (by multiplying).
For example, to solve the problem: 'A man walks 7 miles in 2 hours. How far does he walk in 7 hours?', one would first calculate how far the man walks in 1 hour. One can safely assume that he would walk half the distance in half the time. Therefore, dividing by 2, the man walks 3.5 miles in 1 hour. Multiplying by 7 for 7 hours, the man walks 7x3.5=24.5 miles.
The same method can be applied to the problem: 'A man walks at 4 miles per hour. How long would it take him to cover 5 miles?'. Dividing by 4 shows that the man covers 1 mile in a quarter (0.25) of an hour. Multiplying by 5 shows that the man therefore takes 1 hour and a quarter (1.25 hours) to cover 5 miles.