Aligning decimal points: Align the numbers by their decimal points.When adding decimals, it's important to align the decimal points to ensure that the digits are in the correct place value.
Adding the numbers: Add the numbers.Starting from the rightmost digit, add each column of numbers. If a column adds up to 10 or more, carry over to the next column on the left.\begin{align*}
&0.354 \
+ &8.47 \
\hline
&8.824
\end{align*}We add 4 to 0 to get 4 in the thousandths place, 5 to 7 to get 12, so we write down 2 in the hundredths place and carry over 1 to the tenths place. Then we add 3, 4, and the carried over 1 to get 42 in the tenths place. Finally, we add 0 and 42 to get 42 in the ones place.