Adding and subtracting decimals

About this lesson

Grade 6 › Arithmetic in base ten

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Adding and subtracting decimals

Discover

Ana adds 2.5+1.252.5 + 1.25 and gets 1.501.50. What went wrong?

  1. She lined up the last digits, not the decimal points
  2. Nothing

Key idea

Line up the decimal points.

To add or subtract decimals, line up the decimal points (write zeros to fill empty places), then add or subtract place by place, regrouping when needed: 1 one = 10 tenths, 1 tenth = 10 hundredths.

Worked example

7.3−2.687.3 - 2.68.

7.30−2.687.30 - 2.68
Fill the hundredths.
4.624.62
Regroup.

Your turn, guided

Your turn: 3.4+0.753.4 + 0.75.

4.154.15
3.40 + 0.75.

Practice ★

  1. Compute 27.1+11.8127.1 + 11.81.
  2. Compute 16.8+26.4416.8 + 26.44.
  1. Compute 31−7.331 - 7.3.

Watch out!

Practice ★★

  1. Compute 14.1−3.514.1 - 3.5.
  2. Compute 35.3−3.735.3 - 3.7.

Exit ticket

Three questions to check you have got it.

  1. Compute 27.1+11.8127.1 + 11.81.
  2. Compute 16.8+26.4416.8 + 26.44.
  3. Compute 11.3+22.8511.3 + 22.85.

Summary card

Adding and subtracting decimals

Line up the points; regroup as with whole numbers.

Watch out: never subtract the smaller digit from the larger by habit.

End of the lesson

Next lesson: Multiplying decimals Back to the chapter

Answers: Adding and subtracting decimals

A

  1. 3891100\frac{3891}{100}
  2. 108125\frac{1081}{25}

B

  1. 23710\frac{237}{10}

C

  1. 535\frac{53}{5}
  2. 1585\frac{158}{5}

D

  1. 3891100\frac{3891}{100}
  2. 108125\frac{1081}{25}
  3. 68320\frac{683}{20}

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