Class 8 Chapter 11: Direct and Inverse Proportions

# Class 8 Chapter 11: Direct and Inverse Proportions

Important Concepts and Formulas on Direct and Inverse Proportions

1.    Two quantities are in direct proportion, if the increase in one quantity causes an increase in the other and vice-versa.

2.    If two quantities x and y are in direct proportion, then the ratio of their corresponding values remains constant. For example, x1/y1 = x2/y2

3.      Two quantities are in inverse proportion, if the increase in one quantity causes decrease in the other and vice-versa.

4.      If two quantities x and y are in inverse proportion, then the product of their corresponding values remains constant. For example, x1y1 = x2y2

5.      Speed = Distance/Time; Time = Distance/Speed; Distance = Speed × Time.

6.      If A can do a piece of work in n days, then A’s one day’s work = 1/n of the work.

7.      Number of days to complete the work = 1/One day's work.

8.      Time required to do a certain work = Work to be done/One day's work.