With adding and subtracting decimal numbers the approach is the same as with whole numbers, as can be seen here.
But with decimal numbers we have to remember to include a decimal point in the correct place.
Examples
1.1
1.323 + 2.246
Solution
\begin{array}{r} \space\space\space{\bf{1.323}}\space\space\\ +\space\space{\bf{2.246}}\space\space\\ \hline \space\space\space\space\space\space{\bf{3.569}}\space\space \end{array}
1.2
3.26 + 4.062
Solution
To get the 3 decimal places needed in the first number.
We just write 3.26 as 3.260, as they have the same value.
\begin{array}{r} \space\space\space{\bf{3.260}}\space\space\\ +\space\space{\bf{4.026}}\space\space\\ \hline \space\space\space\space\space\space{\bf{7.286}}\space\space \end{array}
1.3
2.35 + 0.403 + 2
Solution
Like with 3.26 having the same value as 3.260,
2 has the same value as 2.000
\begin{array}{r} \space\space\space{\bf{2.350}}\space\space\\ \space\space\space{\bf{0.403}}\space\space\\ +\space\space {\bf{2.000}}\space\space\\ \hline \space\space\space\space\space\space{\bf{4.753}}\space\space \end{array}
1.4
4.054 − 1.04
Solution
Like with 3.26 having the same value as 3.260, 2 has the same value as 2.000
\begin{array}{r} \space\space\space{\bf{4.054}}\space\space\\ {\text{--}}\space\space{\bf{1.040}}\space\space\\ \hline \space\space\space\space\space\space{\bf{3.014}}\space\space \end{array}
1.6
2.56 + 3.73 − 2.21
Solution
\begin{array}{r} {\tiny{1}}\space\space\space\space\space\space\space\space\\ \space\space\space{\bf{2.56}}\space\space\\ +\space\space{\bf{3.73}}\space\space\\ {\text{--}}\space\space{\bf{2.21}}\space\space\\ \hline \space\space\space\space\space{\bf{4.08}}\space\space \end{array}
1.5
5.676 − 2.13 − 1.1
Solution
\begin{array}{r} \space\space\space{\bf{5.676}}\space\space\\ \space\space\space{\bf{2.130}}\space\space\\ {\text{--}}\space\space{\bf{1.100}}\space\space\\ \hline \space\space\space\space\space\space{\bf{2.446}}\space\space \end{array}
1.7
3.604 + 1 − 2.31
Solution
\begin{array}{r} \space\space\space{\bf{3.604}}\space\space\\ {\text{--}}\space\space{\bf{1.000}}\space\space\\ +\space\space{\bf{2.310}}\space\space\\ \hline \space\space\space\space\space{\bf{4.914}}\space\space \end{array}
Adding and Subtracting Decimal Numbers,
Further Examples
2.1
A person has $60.23 in a banking account. One day they decide to withdraw $32.12,
then the next day they decide to pay in $15.24.
How much money is in the account after those 2 days?
Solution
\begin{array}{r} \space\space\space{\bf{60.23}}\space\space\\ {\text{--}}\space\space{\bf{32.12}}\space\space\\ +\space\space{\bf{15.24}}\space\space\\ \hline \space\space\space\space\space{\bf{43.35}}\space\space \end{array}
There was $43.35 in the persons banking account after the 2 days.
2.2
A thermometer in a garage measured different temperatures through out a day.
In the early morning the temperature was 3.6°C.
While in the afternoon the temperature was 15.4°C.
How much did the temperature in the garage increase from the morning to the afternoon.
Solution
\begin{array}{r} {\footnotesize{4}}\space\space\space\space\space\space\space\space\\ \space\space\space{\bf{1{\cancel{5}}.^{{\tiny{1}}}4}}\space\space\space\\ {\text{--}}\space\space\space\space{\bf{3.6}}\space\space\space\space\\ \hline \space\space\space{\bf{11.8}}\space\space\space\space \end{array}
The temperature in the garage increased by 11.8°C from morning to afternoon.
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