Math CentralQuandaries & Queries


Question from Keith, a parent:

how are decimals used in every day life

Hello Keith,

There are a great variety of numbers in the world and all have their place and purpose.  We live in an imperfect world, so approximation of many of these numbers is sufficient.  For example, π is a very important number, a so called irrational number, meaning that it cannot be written as a fraction (rational number).  To make calculations we approximate it, say as π ≈ 3.14. All irrational numbers can be approximated to a suitable degree by some fraction.  This means that the only numbers we must use in life are the rational numbers (but we would miss out on a great many things).

Decimal representations for numbers are used all the time in our everyday lives.  A reason for this is that they are much easier to “visualize” than fractions.  Eight fifths of a dollar for a chocolate bar seems like a rather odd way of saying that a chocolate bar costs $1.60 (8/5 = 1.6).  We use decimals because they are easier to compare with.  For instance, it is much easier for me to confirm that 3.75 is smaller than 3.8 but not so clear to confirm that 15/4 is smaller than 19/5. Nowadays we are accustomed to working with decimals instead of fractions but this was not always the case.

The bulk of the use of decimal representations is with money and the economy.  Can you think of other situations where these are used?

The next time you are at the store try to imagine the price tags written as fractions instead of decimals.

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