To multiply two-digit decimals, we can use the usual method of removing and replacing the decimal point.
As an example, let's learn how to compute We proceed as follows:
Step 1. First, ignore the decimal points and multiply as if both numbers were whole numbers:
Step 2. Then, insert the decimal point in the result so that number of decimal places is equal to the total number of decimal places in both factors combined.
Here, there is decimal place in and there is decimal place in so their product will have a total of decimal places.
We take our value of and insert a decimal point to make a number with decimal places:
Notice that both numbers have the leading zeros, which we ignore during the multiplication.
We proceed by multiplying the two numbers just as we would with whole numbers. So,
\[
3 \times 7 = 21.
\]
We now count the total number of decimal places in the two factors.
There is $\color{blue}1$ decimal place in $0.3$ and there is $\color{blue}1$ decimal place in $0.7.$
Therefore, their product will have ${\color{blue}1} + {\color{blue}1} = 2$ decimal places.
So, we take our value of $21$ and add a decimal point to make a number with $2$ decimal places.
First, we ignore the decimal point and multiply as if both numbers were whole numbers:
\[
8 \times 7 = 56.
\]
We now count the total number of decimal places in the two factors.
There is $\color{blue}1$ decimal place in $0.8$ and there is $\color{blue}1$ decimal place in $0.7,$ so their product will have ${\color{blue}1} + {\color{blue}1} = 2$ decimal places.
We take our value of $56$ and insert a decimal point to make a number with $2$ decimal places:
We now count the total number of decimal places in the two factors.
There is $\color{blue}1$ decimal place in $1.4$ and there is $\color{blue}1$ decimal place in $0.9.$
Therefore, their product will have ${\color{blue}1} + {\color{blue}1} = 2$ decimal places.
So, we take our value of $126$ and add a decimal point to make a number with $2$ decimal places.
First, we ignore the decimal points and multiply as if both numbers were whole numbers:
\[
\begin{align*}
\require{cancel}
%%%%%%%%%%
%%% Step A %%%
%%%%%%%%%%
&
\begin{array}{ccccc}
& & & \!\!\!\!\! \color{lightgray} \substack{ \fbox{$\color{blue}2$} \\[2pt] \fbox{$\color{blue}3$} } \!\!\!\! & \\
& & & \!\!\!\! 0 \!\!\!\! & \!\!\!\!\!\!\! . 7 \!\!\!\! \\
\!\!\!\!\times\!\!\!\! & \!\!\!\!\phantom{0}\!\!\!\! & \!\!\!\!\phantom{0}\!\!\!\! & \!\!\!\! 3 \!\!\!\! & \!\!\!\!\!\!\! . 5 \!\!\!\! \\
\hline
& & \!\!\!\! \!\!\!\! & \!\!\!\! 3 \!\!\!\! & \!\!\!\! 5 \!\!\!\! \\
\!\!\!\!+\!\!\!\! & \!\!\!\! \!\!\!\! & \!\!\!\! 2 \!\!\!\! & \!\!\!\! 1 \!\!\!\! & \!\!\!\! 0 \!\!\!\! \\
\hline
& \!\!\!\! \!\!\!\! & \!\!\!\! 2 \!\!\!\! & \!\!\!\! 4 \!\!\!\! & \!\!\!\! 5 \!\!\!\! \\
\end{array}
\end{align*}
\]
We now count the total number of decimal places in the two factors.
There is $\color{blue}1$ decimal place in $0.7$ and there is $\color{blue}1$ decimal place in $3.5,$ so their product will have ${\color{blue}{1}} + {\color{blue}{1}} = 2$ decimal places.
We take our value of $245$ and insert a decimal point to make a number with $2$ decimal places.
We now count the total number of decimal places in the two factors.
There is $\color{blue}1$ decimal place in $5.4$ and there is $\color{blue}1$ decimal place in $1.3.$
Therefore, their product will have ${\color{blue}{1}} + {\color{blue}{1}} = 2$ decimal places.
So, we take our value of $702$ and add a decimal point to make a number with $2$ decimal places.
We now count the total number of decimal places in the two factors.
There is $\color{blue}1$ decimal place in $4.3$ and there is $\color{blue}1$ decimal place in $8.7,$ so their product will have ${\color{blue}{1}} + {\color{blue}{1}} = 2$ decimal places.
We take our value of $3741$ and insert a decimal point to make a number with $2$ decimal places:
We now count the total number of decimal places in the two factors.
There is $\color{blue}1$ decimal place in $1.4$ and there is $\color{blue}1$ decimal place in $1.6,$ so their product will have ${\color{blue}{1}} + {\color{blue}{1}} = 2$ decimal places.
We take our value of $224$ and insert a decimal point to make a number with $2$ decimal places:
We now count the total number of decimal places in the two factors.
There is $\color{blue}1$ decimal place in $7.2$ and there is $\color{blue}1$ decimal place in $8.5,$ so their product will have ${\color{blue}{1}} + {\color{blue}{1}} = 2$ decimal places.
We take our value of $6120$ and insert a decimal point to make a number with $2$ decimal places: