Estimate sums and differences of decimals

Learning Objectives Define estimation and explain its purpose in mathematics. Round decimals to the nearest whole number. Round decimals to a specified decimal place (e.g., nearest tenth). Estimate the sum of two or more decimals by rounding. Estimate the difference between two decimals by rounding. Determine if an exact answer is needed or if an estimate is sufficient in a given real-world context. Have you ever needed to quickly figure out about how much money you'll spend at the store without using a calculator? 🛒 That's where estimating comes in handy! In this lesson, you'll learn how to make smart guesses, or estimates, when adding and subtracting decimals. This skill helps you check if your exact answers are reasonable and makes quick calculations easi...

TermDefinitionExample EstimationFinding a value that is close enough to the correct answer, often used when an exact answer isn't necessary or to check the reasonableness of an exact answer.Estimating that 3.95 + 5.10 is about 4 + 5 = 9. RoundingReplacing a number with an approximate value that is simpler or easier to work with, usually to a specific place value.Rounding 7.8 to the nearest whole number gives 8. Whole NumberA number without fractions or decimals (e.g., 0, 1, 2, 3...).In the number 12.34, 12 is the whole number part. Decimal Place ValueThe position of a digit to the right of the decimal point, such as tenths, hundredths, thousandths.In 0.75, the 7 is in the tenths place and the 5 is in the hundredths place. SumThe result of adding two or more numbers together.The sum o...

Rule for Rounding Decimals to a Whole Number To round a decimal to the nearest whole number, look at the digit in the tenths place. If it is 5 or greater, round the whole number up. If it is less than 5, keep the whole number the same. This rule helps simplify decimals for quick estimation by turning them into whole numbers. For example, $4.7 \approx 5$ and $4.2 \approx 4$. Rule for Rounding Decimals to a Specific Place Value To round a decimal to a specific place value (e.g., the nearest tenth), look at the digit immediately to its right. If that digit is 5 or greater, round the digit in the target place value up. If it is less than 5, keep the digit in the target place value the same. Drop all digits to the right of the target place value. Use this rule when you need a sli...