Final answer:
To estimate the sum of 5.5 + 4.2, round each number to the nearest whole number and then add them together.
Step-by-step explanation:
To estimate the sum of 5.5 + 4.2, you can round each number to the nearest whole number. 5.5 rounds to 6, and 4.2 rounds to 4. Then, you can add these rounded numbers together to get an estimate of the sum, which is 10.