# Ratio and proportion. Proportionality

*Ratio. Proportion ( border and middle terms ).*

The main property of a proportion.

Proportional values. Factor of a proportionality.

The main property of a proportion.

Proportional values. Factor of a proportionality.

* Ratio is a quotient of dividing one number by another.
Proportion – an equality of two ratios. * For instance:

12 : 20 = 3 : 5; *a : b = c : d .*

*Border terms of the proportion: * 12 and 5 in the first proportion;

*a* and *d * in the second proportion.

*Middle terms of the proportion: * 20 and 3 in the first proportion;

*b* and *c* in the second proportion.

**The main property of a proportion: **A product of border terms of a proportion is equal to a product of its middle terms.

*Two mutually dependent values are called proportional ones, if a ratio of their values is saved as invariable. *This invariable ratio of proportional

values is called a

*.*

**factor of a proportionality**

E x a m p l e . | A mass of any substance is proportional to its volume. For instance, 2 liters of mercury weigh 27.2 kg, 5 liters weigh 68 kg, 7 liters weigh 95.2 kg. A ratio of mercury mass to its volume ( factor of a proportionality ) will be equal to: Thus, a factor of a proportionality in this example is density. |