A quantity can be defined as how much of something there is, or as an amount. Quantity can also be used to refer to the size of something (its magnitude), whether in terms of numbers, units of measurement, or just relative size. Quantities can be compared; there can be more of one quantity than another, less of one quantity, or two quantities can be equal.
A quantity can have a measured value, such as mass (1 pound), time (12 minutes), distance (7 miles), temperature (35 °C), and more.
Quantities don't necessarily need to have a numerical value. Examples include an army of people or a flock of birds. While there can be a number associated with both of these, there does not have to be in order for them to be considered quantities.
Quantities in math
Quantities are used in virtually all areas of mathematics. Above were some examples of quantities in everyday life that could also be applied to mathematics. Below are some others.
Quantities in algebra
A quantity can be used to describe an unknown amount, as in an algebraic equation. For example, "if five plus some quantity, x, equals 17, what is x?" This phrase can be written algebraically as follows:
5 + x = 17
x = 17 - 5 = 12
Using arithmetic, equality, and an understanding of quantities, we can find answers to questions such as the one posed above.
Quantities in geometry
There are many different quantities in geometry. Some of these include the measure of an angle, such as an acute angle that measures 36°. The length of the sides of a square also has a quantity, or magnitude, from which we can find even more quantities. For example, the square shown below has a side length of 3 centimeters.
3 centimeters is a quantity in itself, but we can also find the area of the square to be 9 cm2, which is another quantity.
These are just a few examples of quantities. There are many more in both everyday life as well as mathematics.