Add and subtract decimals

Key Notes:

Understanding Decimals

• A decimal number consists of a whole number part and a fractional part separated by a decimal point.
• Example: 12.34 (whole number: 12, fractional part: 0.34).

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Place Value in Decimals

• Place values to the right of the decimal point are tenths, hundredths, thousandths, etc.
• Example: In 5.678, 5 is the whole number, 6 is in the tenths place, 7 is in the hundredths place, and 8 is in the thousandths place.

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Steps to Add Decimals

• Step 1: Align the decimal points of the numbers to be added.
• Step 2: Add zeros to make the number of decimal places equal if necessary.
• Step 3: Add as you would whole numbers, starting from the rightmost digit.
• Step 4: Place the decimal point in the sum directly below the decimal points of the numbers.
• Example:
  12.34+5.678=12.340+5.678=18.018.

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Steps to Subtract Decimals

• Step 1: Align the decimal points of the numbers to be subtracted.
• Step 2: Add zeros to make the number of decimal places equal if necessary.
• Step 3: Subtract as you would whole numbers, starting from the rightmost digit.
• Step 4: Place the decimal point in the result directly below the decimal points of the numbers.
• Example:
  15.6−3.475=15.600−3.475=12.125.

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Key Rules

• Always line up the decimal points when adding or subtracting decimals.
• Fill in missing places with zeros to avoid confusion.
• Double-check the placement of the decimal point in the final answer.

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Practical Applications

• Money: Adding or subtracting prices or amounts (e.g., $23.45+$6.78=$30.23).
• Measurements: Calculating lengths, weights, or volumes in decimal form (e.g., 12.5 cm+8.75 cm=21.25 cm).

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Common Mistakes to Avoid

• Misaligning decimal points.
• Forgetting to fill in missing digits with zeros.
• Incorrect placement of the decimal point in the answer.

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Practice Problems

• Add: 7.32+0.568
• Subtract: 9.004−2.78
• Solve real-life problems involving adding and subtracting decimals.

Let’s practice!