**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, x

_{1}/y_{1}= x_{2}/y_{2}_{}
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, x

_{1}y_{1}= x_{2}y_{2}_{}
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.

To study about direct and inverse proportions in detail ----- Click Here!

To study about direct and inverse proportions in detail ----- Click Here!