This video shows the method to solve word problems using proportions. In the given problem, we have to find the time taken by a person to type 390 words if the person takes 1 minute to type 30 words. This can be solved using proportions. We take two fractions which are equal. We type '30 words' in the numerator of the first fraction and 1 minute in its denominator. This fraction must be proportional to the second fraction. The second fraction has '390 words' in the numerator and the variable 'x' to represent the time which we have to find. This can be written as (30 words)/(1 minute)=(390 words)/(x minutes). Cross multiplying we get 30x=390 or x=13 minutes. Thus the final answer is 13 minutes.