Why do the decimal points have to line up?

Because addition adds like places to like places. Lining up the points is just the way to make sure tenths sit under tenths and hundredths under hundredths.

Can we add a zero on the end?

Yes, freely. A trailing zero after the decimal point does not change the value and it makes the columns match, which prevents most alignment errors.

Can I change how many problems are on the page?

Yes — the generator takes 10, 20 or 30 problems. Twenty is the default because it fits one page and suits a 10-minute drill.

Is the answer key included?

Yes, on its own page behind the worksheet. For the sheet loaded right now it shows 17.1 for 4.9 + 12.2 and 26.5 for 10.8 + 15.7.

Worksheets › adding decimals to one place

Adding Decimals to Tenths

This page makes free printable adding decimals tenths worksheets on demand: press the button and you get a new sheet of 20 problems with a matching answer key, ready for US Letter or A4 paper. A typical problem from the sheet in front of you is 4.9 + 12.2, which works out to 17.1; another is 10.8 + 15.7, giving 26.5.

📄 ADDING DECIMALS TENTHS — A NEW SHEET EVERY TIME YOU PRESS THE BUTTON

🎲 New set of problems

‘New set of problems’ opens the generator in its own tab. There you can change the problem count and turn the answer key on or off. ‘Print or save as PDF’ opens the print dialog — choose Save as PDF in the printer list to keep the file. The sheet fits US Letter and A4, and the answer key prints on its own page.

What the sheet contains

This is where place-value understanding gets tested. To a child who really understands 17.8 + 12.0, the tenths column is not 'the first column after the point' — it is a place worth a tenth.

This sheet uses one-place decimals up to 19.9, with two decimal places, which is the form children meet most often in money and measurement — 12.0 + 17.9 is a fair example of it.

Because the numbers regenerate, the alignment has to be handled fresh each time rather than copied from a previous layout.

Estimation is the check that works best here. Rounding each number in 10.8 + 15.7 to the nearest whole gives a total that 26.5 has to be close to.

In US classrooms these adding decimals tenths worksheets are commonly aligned with the decimal operations expectations for grade 5, though the exact wording varies from state to state.

A sample of this sheet, with answers

These six come from the sheet loaded on this page. Press the button and the numbers change, but the shape stays the same (one-place decimals up to 19.9).
#	Problem	Answer	What to check
1	4.9 + 12.2 =	17.1	Watch for: lining the numbers up on the right
2	10.8 + 15.7 =	26.5	Check: forgetting the trailing zero
3	17.8 + 12.0 =	29.8	Look at: regrouping across the decimal point incorrectly
4	2.2 + 12.4 =	14.6	Ask about: losing the decimal point in the answer
5	12.0 + 17.9 =	29.9	Watch for: not estimating
6	1.3 + 16.2 =	17.5	Check: treating the two sides of the point as separate numbers

Start with one worked example

Work 2.2 + 12.4 out loud as a demonstration. It gives 14.6. Children who hear 2.2 + 12.4 reasoned through once at the start of a session make noticeably fewer errors in the ten minutes that follow.

The item 10.8 + 15.7 is worth doing slowly. The answer to 10.8 + 15.7 is 26.5, and the route to it is the route every other problem on this sheet takes — which is why the sheet has 20 of them rather than one.

Three mistakes we see most often

Forgetting the trailing zero
Not an error by itself, but it makes misalignment much more likely for children who are still learning the layout.
Treating the two sides of the point as separate numbers
Adding the whole parts and the decimal parts independently works until the decimal part carries over, and then it fails silently.
Regrouping across the decimal point incorrectly
The carry crosses the point exactly like any other column. Children often stop the carry at the point instead.

Getting the most out of 10 minutes a day

Keep the session to about 10 minutes. A child working at this level who is still counting on fingers will need longer than that on a line like 4.9 + 12.2, and that is fine: the timer is a measurement, never a punishment.
Read the first two problems out loud together before starting the clock. It costs fifteen seconds and removes most of the 'I did not understand the question' errors.
Mark it together straight away while the working is still fresh, so a slip like the one behind 17.8 + 12.0 can be talked through instead of guessed at.
Stop the session at the time limit even if the sheet is unfinished, and note where the child got to. A half sheet done well is better data than a whole sheet rushed.
Re-print the same skill rather than the same sheet. Because the numbers change, a child who memorised that 4.9 + 12.2 gives 17.1 still has to actually calculate tomorrow.

About the answer key

The key prints on its own page by default. Uncheck the answer-key box before printing if you would rather keep it back and mark the sheet yourself.

The answer key is generated with the worksheet, not written by hand, so it always matches the sheet in front of you — 4.9 + 12.2 is listed as 17.1, 10.8 + 15.7 as 26.5, and so on down the page.

Printing and saving as PDF

If the problems look cramped, drop the count from 20 to a smaller number before printing these adding decimals tenths worksheets; the font stays the same size and the spacing opens up.

Portrait orientation is what the sheet is designed for. Landscape works but wastes about a third of the paper, so leave the orientation alone unless you have a reason.

Frequently asked questions

Why do the decimal points have to line up?: Because addition adds like places to like places. Lining up the points is just the way to make sure tenths sit under tenths and hundredths under hundredths.
Can we add a zero on the end?: Yes, freely. A trailing zero after the decimal point does not change the value and it makes the columns match, which prevents most alignment errors.
Can I change how many problems are on the page?: Yes — the generator takes 10, 20 or 30 problems. Twenty is the default because it fits one page and suits a 10-minute drill.
Is the answer key included?: Yes, on its own page behind the worksheet. For the sheet loaded right now it shows 17.1 for 4.9 + 12.2 and 26.5 for 10.8 + 15.7.

Print a sheet of adding decimals tenths worksheets, run it for 10 minutes, mark it together, and come back tomorrow for a different set of numbers on the same skill.

More worksheets like this

→ Free Decimals Worksheets

Free printable math worksheets from a working math academy director in Korea. Problems come from our own code, not from a published workbook. Every sheet prints on US Letter or A4 with its answer key. All worksheets · Worksheet generator · Korean site
Last updated: 2026-09-13