Add and subtract decimals: word problems
key notes :
Understanding Decimals
- Decimals represent parts of a whole, using place values like tenths, hundredths, and thousandths.
- Example: 3.45 means 3 ones, 4 tenths, and 5 hundredths.
Identifying Key Information
Read the word problem carefully.
Identify numbers with decimals and the operation (addition or subtraction) required.
Look for keywords:
- Addition: total, sum, altogether, in all
- Subtraction: difference, how much more/less, left, remain
Aligning Decimal Places
- Write numbers vertically, ensuring the decimal points are aligned.
- Add placeholder zeros if necessary to match decimal places.
Performing Addition and Subtraction
- Add or subtract like whole numbers.
- Keep the decimal point in the same position in the answer.
Solving Real-World Problems
- Apply decimal operations to money, measurements, and distances.
- Example: If a pencil costs $1.25 and an eraser costs $0.75, find the total cost.
Checking the Answer
- Estimate before solving to check reasonableness.
- Recalculate if the answer does not match expectations.
Learn with an example
A carpenter bought a piece of wood that was 8.6 centimeters long. Then she sawed 1.8 centimeters off the end.
How long is the piece of wood now?
Subtract the number of centimeters. Remember to line up the decimal points.
8.6 – 1.8 = 6.8
The piece of wood is 6.8 centimeters long now.
Dominic had 0.21 grams of pepper. Then he used 0.18 grams of pepper to make some scrambled eggs.
How much pepper does Dominic have left?
Subtract the numbers of grams. Remember to line up the decimal points.
0.21 – 0.18 = 0.03
Dominic has 0.03 grams of pepper left.
Cooper bought a piece of fabric that was 9.82 meters long. Then he cut 7.05 meters of it off to use in a sewing project.
How much fabric is left?
Subtract the numbers of grams. Remember to line up the decimal points.
9.82 – 7.05 = 2.77
2.77 meters of fabric are left.
Let’s practice!
