Add and Subtract Multi-Digit Decimals

Students fluently add and subtract decimals to any place value by aligning decimal points and applying the standard algorithm. They estimate to verify the placement of the decimal point in their answer and solve real-world problems involving decimal addition and subtraction.

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Grade 6 · Number System: Multi-Digit Computation · question 1 of 3

0 of 20

20 rungs. A star at the top.

3.25 + 1.4 =

How it is taught

0:00 of 5:37

Line up the decimal points, not the last digits.

A placeholder zero keeps each place honest.

Read it: Decimals, place by place

3.2 + 0.13: line up the points, so the tenths sit under the tenths. 3.2 has no hundredths, so write it as 3.20. Then add by place, as with whole numbers: 3.33.

Put the points in one column, so each place sits under the same place.
Write 0s in the empty places, so both numbers have the same places.
Add or subtract by place from the right, as with whole numbers; the point comes straight down.

3.20 is 320 hundredths and 0.13 is 13 hundredths: 320 + 13 = 333 hundredths, which is 3.33.

Writing a 0 at the end does not change a decimal: 3.2 and 3.20 are the same number.

10 hundredths make 1 tenth, so you regroup across the point just as with whole numbers.

Points under points, 0s in the empty places, then add or subtract by place.

Lining up the last digits instead of the points, and getting 0.45.

Line up the points: 3.20 + 0.13 = 3.33.

3 + 0.44 = ___ — 3.44. Points under points, 3 written 3.00: 3.44.

12.7 + 3.45

You have twelve dollars and seventy cents, and you earn three dollars and forty-five cents walking a dog. How much money do you have now?

We can solve this by stacking the numbers and adding column by column.

First let's estimate. Twelve point seven rounds to thirteen, plus three is about sixteen — so our answer should land near sixteen.

The most important step: line up the decimal points so each place value sits in its own column.

Twelve point seven has nothing in the hundredths place, so we write a zero there as a placeholder.

Start on the right. Zero plus five equals five.

Tenths column: seven plus four is eleven. Write the one, and carry the other one to the ones place.

Ones column: two plus three plus the carried one is six.

Tens column: just one — bring it down.

Now drop the decimal point straight down so it lines up with the others.

Grade 6 · Line up the decimal points

Twelve point seven plus three point four five equals sixteen point one five — right around our estimate of sixteen. Great work!

What you see

While they climb, your page writes one true line to ask about tonight, and a short note each Sunday.

MayaGrade 3 · Mathematics

Did you know?

A chessboard has 64 squares — share them out between the 8 rows and each row holds exactly 8.

Today’s goal: 1 star — one skill mastered, every rung of its ladder climbed
Climbing now: Divide within 100

An example student.

MayaGrade 3 · Mathematics

Maya earned 2 stars this week — Interpret multiplication as equal groups, which took 6 answers over 3 days before its star landed 3 days ago and Multiply by 6, 7, 8 and 9. Next up: Divide within 100.

An example week.

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