Operations with decimals

Topic summary

When adding or subtracting decimals, align the decimal points and then perform the operation as you would with whole numbers. When multiplying, convert the decimals to whole numbers and then times. Don’t forget to convert them back. When dividing, use the bus stop method.

Adding and subtracting decimals

\[12.34 + 5.67\]

Use the column method for adding and subtracting decimals.

\begin{align} 12.34& \\ \underline{+\quad 5.67}& \\ 18.01& \end{align}

Multiplying decimals

\[1.2 \times 0.35\]

Multiply each decimal by a power of 10 (10, 100, 1000) to convert to whole numbers.

\[1.2 \times 10 = 12\]

\[0.35 \times 100 = 35\]

Multiply the whole numbers.

\[12 \times 35 = 420\]

Undo the \(\times 10\) and \(\times 100\) using division.

\[420 \div 10 \div 100 = 0.42\]

Dividing decimals

Use the bus stop method. Make sure to add zeros after the decimal point if needed.