## CBSE Class 8 Maths Chapter 13 Notes Direct and Indirect Proportions

### Direct and Indirect Proportions Class 8 Notes Conceptual Facts

1. The two quantities are said to be directly proportional if

- an increase in one leads to a corresponding increase in the other.
- a decrease in one leads to a corresponding decrease in the other.

2. If x varies directly as y then the ratio \(\frac{x}{y}=k\) (constant) symbolically, x α y, where α is symbol of

proportionality or x = ky \(\frac{x_{1}}{y_{1}}=\frac{x_{2}}{y_{2}}=\frac{x_{3}}{y_{3}}=k\)

3. The two quantities are said to be inversely proportional if

- an increase in one leads to a corresponding decrease in the other.
- a decrease in one leads to a corresponding increase in the other.

4. If x varies inversely with y, then x α \(\frac{1}{y}\) ⇒ xy = k(constant) or xy – x_{1}y_{1} = x_{2}y_{2} = k.

5. Speed =\(\frac{\text { Distance }}{\text { Time }} \) or Distance = Speed x time or time =\(\frac{\text { Distance }}{\text { Speed }}\)