Math practice · reimagined
Decimals Game
This decimal math game climbs from tenths to hundredths, like 3.5 − 0.33, and ends by multiplying a decimal by a whole number, as in 4.9 × 9. You and your rival race on the same numbers, and the first right answer throws the punch.
Ages 4–99+ · no download · plays in your browser · 23 languages
What are decimals?
Decimals are numbers that use a point to show parts smaller than one. Each place after the point is ten times smaller than the place before it: first tenths, then hundredths. Cut a cake into 10 equal slices, and each slice is 0.1 of it. Cut one slice into 10 thin pieces, and each piece is 0.01.
Example: what is 3.5 − 0.33?
- Here 3.5 has one digit after the point and 0.33 has two, so give 3.5 a zero and write 3.50.
- That zero changes nothing, because 5 tenths are the same amount as 50 hundredths.
- Now count both numbers in hundredths: 350 − 33 = 317 hundredths.
- 317 hundredths make 3.17, so you type 3.17 on the keypad.
Learn it step by step
A decimal point splits a number into whole parts and tiny parts — tenths, hundredths — like the cents after the dollars in a price.
To add or subtract them, the golden rule is to line the dots up so tenths sit under tenths. Then it's ordinary adding: 0.3 + 0.4 = 0.7, just like 3 + 4 = 7 but a size smaller. Watch for carries the same way — 0.7 + 0.5 = 1.2, because the tenths spilled over into a whole.
Keep the point in the same spot in your answer, and type the result.
Tips and common mistakes
- Before you type, round to whole numbers for a quick check. 4.9 × 9 is close to 5 × 9 = 45, so 44.1 makes sense and 4.41 does not.
- A common mistake is lining up the last digits instead of the points. Done that way, 6.41 + 1.4 gives 6.55, but lined up by the points it is 7.81.
- Measure two things at home in metres, such as a table 1.25 m long and a shelf 0.8 m long. Then ask how much longer the table is: 0.45 m.
How to play
Each problem shows decimals such as 8.1 − 7.2, 6.41 + 1.4 or 0.6 × 7, and you type the result with the keypad’s decimal key. Some answers come out whole, like 7.7 + 4.3 = 12, so no point is needed. Be first and Chilli attacks, with a stronger hit for a quicker answer.
— Quick answers —
Decimals: the short FAQ
- What are tenths and hundredths?
- Tenths and hundredths are the first two places after the decimal point. A tenth is one whole split into 10 equal parts, written 0.1. A hundredth is one whole split into 100 equal parts, written 0.01, so ten hundredths make one tenth. In 2.46 there are 2 wholes, 4 tenths and 6 hundredths.
- How do you multiply a decimal by a whole number?
- You multiply as if the point were not there, then put it back with as many digits after it as the decimal had. For 2.7 × 4, work out 27 × 4 = 108. The 2.7 had one digit after its point, so the answer is 10.8. Adding 2.7 four times gives the same 10.8, which confirms it.
- Is there a trick for adding decimals in your head?
- Yes, add the wholes and the tenths separately, then join the two results. For 3.6 + 2.7, the wholes give 3 + 2 = 5 and the tenths give 0.6 + 0.7 = 1.3. Together that makes 5 + 1.3 = 6.3. Splitting the numbers this way keeps the point in its place without writing anything down.
- Why does my child think 0.35 is bigger than 0.5?
- Many children read the digits after the point as a whole number, and 35 looks bigger than 5. Writing both numbers with the same count of digits clears it up: 0.5 becomes 0.50, and 50 hundredths are more than 35 hundredths. On a number line from 0 to 1, 0.5 sits in the middle and 0.35 comes before it.
- Does this decimal math game cost anything for a class?
- No, all three decimal levels are free, and a web browser is all each pupil needs, with no install and no account. For a burst of decimal practice, write 1.8, 2.75, 3.2 and 2.25 on the board and ask pupils to find the two pairs that make exactly 5. After that, each pupil fights alone on a tablet. The schools plan, priced per student, adds a teacher dashboard showing who is getting better at decimals.