To add decimals, line up the decimal points so that place-value positions correspond.
521.52
Practice makes perfect
Before we find the exact sum, we can make an estimate by rounding each addend. We will round 423.22 to 423 and 98.30 to 98 because they are the closest whole numbers.
423+98=521
The sum of 423.22 and 98.30 is about 521. Now we can find the exact sum. To add decimals, we line up the decimal points so that place-value positions correspond.
Now we add the decimals, just as we would with whole numbers, and place the decimal point in the answer.
The answer 521.52 is really close to our estimation!