Add and subtract decimals: word problems

key notes :

Understanding Decimals

• Decimals represent parts of a whole number.
• Place value is important (tenths, hundredths, thousandths, etc.).

Addition of Decimals

• Align decimal points before adding.
• Add digits column by column, carrying if necessary.
• Keep the decimal point in the same position in the sum.

Subtraction of Decimals

• Align decimal points before subtracting.
• Borrow when needed, just like whole numbers.
• Keep the decimal point in the same position in the difference.

Word Problem Strategies

• Read the problem carefully and identify the question.
• Determine if it requires addition or subtraction.
• Identify key phrases like “total,” “sum,” “difference,” “how much more/less,” etc.
• Convert mixed units (e.g., dollars and cents) into decimals if needed.

Real-Life Applications

• Money-related problems (e.g., shopping bills, discounts, taxes).
• Measurement problems (e.g., lengths, weights, capacities).
• Data-related problems (e.g., temperature changes, distance covered).

Checking the Answer

• Estimate to check if the answer is reasonable.
• Recalculate using reverse operations (e.g., check subtraction by adding).
• Ensure the decimal is placed correctly.

Common Mistakes to Avoid

• Misaligning decimal points when adding or subtracting.
• Forgetting to add zeros to match decimal places.
• Incorrect borrowing or carrying.
• Ignoring the decimal point in the final answer.

Learn with an example