Place Value

The figures in a decimal have a value, depending on their place in the number.

The value is given by the following headings:

The first figure 5 is 5 units because it is in the units column.

The second figure 5 is 5 hundredths because it is in the hundredths column.

When working with decimals, it is important to keep the figures in the correct columns.

Adding and Subtracting Decimals

Rule: Keep the points in line and add or subtract in columns.

Example: 6,23 + 17,58 + 0,452

Back to top

Multiplying Decimals

a. Short multiplication

Done in the same way as integers but putting in the decimal comma as we reach it.

b. Long multiplication

We do this in the same way as long multiplication of integers. Then put the decimal comma in the answer, in the following way.

4,32 has two figures after the comma.

5,2 has one figure after the comma.

2 + 1 = 3, which gives the number of figures after the point in the answer.

Back to top

Division of Decimals

a. Dividing a decimal by a whole number (an integer)

Done in the same way as dividing integers but keep the decimal point in line in the answer.

Example:	12,45 ÷ 5	= 2,49
		^
		commas in line

We make the 0,5 into a whole number by multiplying by 10. We must also do the same to the 6,25.

62,5 ÷ 5 = 12,5

Rule: To divide by a decimal, we must make it into a whole number by multiplying by 10, 100, etc. We must multiply the other number by the same amount.

We can deal with remainders: 17 ÷ 4 = 4,25.

   As many zeros as we need can be added after the decimal point and we continue to divide as for whole numbers.

Back to top

Note: We can use a simple rule to describe these results.

The point moves by the same number of places as there are zeros.

It moves to the right for multiplication and to the left for division.

Put the decimal over its last heading:

Back to top
Print this page