Åk 6–9

1.2 Why do we need decimals?
The need to be able to write parts of a whole started early. People began first by using fractions. When the decimal system was introduced, we began also expressing parts as decimals.

Now we are used to using decimals everyday and often without thinking about it.

When we express distances and heights, we often do so using decimal numbers. For example, It is 1.5 km to the school or Kalle is 1.72 m tall.

Here are two examples:

 When we shop, the price often expressed in decimal numbers for example 6.50 kr. Foto: Fredrik Enander

 Many times it involves time.  Erik ran the hundred meter dash in 11.52 s. Foto: Nils Sundberg, Multimediabyrån

A decimal number often contains two parts.  The decimal sign is used to separate the whole number part and the decimal part. In Swedish, like Arabic, French and German, we use the comma (,) as a decimal sign but certain other languages use the point (.) or even the half high point (·) instead, predominantly in English speaking literature.  The half high point is not preferred because it can be easily confused with the multiplication sign.  In Spanish, the comma (,) is used but in certain literature even the ´ (ex 4´57) can be found.

A decimal sign is written closely next to those numbers to which it belongs:
674.56
not with a space in between
674 . 56

When decimals are less than 1, we sometimes do not write out the zero, but instead write the decimal sign followed by the decimal digits.  This is used predominantly in English and is not recommended because confusion can easily occur:  0.56 = .56

When you read decimals, you can do so in many different ways.  The number 4,57 can be read as:

• "4 comma 57"
• "4 wholes and 57 hundredths"
• "4 wholes, 5 tenths and 7 hundredths"
• "4 and 57"

We recommend that you, in the beginning, read the number as ”4 wholes and 57 hundredths” or ”4 wholes, 5 tenths, and 7 hundredths”.  This gives a better understanding for the size of the number.