Quick Notes

Compare Decimals:

Example of question: Which mass is heaviee, 0.45 kg or 0.2 kg?

Compare the tenths digits. 4 is larger than 2.

So, 0.45 kg is larger than 0.2 kg.

Addition of Decimals:

The height of shelf A is 0.5 m while the height of shelf B is 0.3 m What is the total height of this shelf?

Mathematical sentence: \(0.5\space\text{m}\space+\space0.3\space\text{m}=\underline{\quad\quad}\)

Method:

\(\begin{array} {rr} \space\space\space0\space.\space5\space\text{m} \\+\space\space\space0\space.\space3\space\text{m} \\\hline\space\space\space0\space.\space8\space\text{m} \\\hline \end{array}\)

Tips: Arrange the digits. Make sure that the decimal point is alligned.

Substraction of Decimals:

A board 0.7 m long was cut by 0.2 m to make a chair. What is the length of the wooden plank after it is cut?

Mathematical sentence: \(0.7\space\text{m}\space-\space0.2\space\text{m}=\underline{\quad\quad}\)

Method: 

\(\begin{array} {rr} \space\space\space0\space.\space7\space\text{m} \\-\space\space\space0\space.\space2\space\text{m} \\\hline\space\space\space0\space.\space5\space\text{m} \\\hline \end{array}\)

Tips: Arrange the digits. Make sure that the decimal point is alligned.