How to use it in 3 steps
- Enter the top number and bottom number. You can paste full-width digits or locale-style decimal input.
- Open Options to show carries, decimal-place cards, and decimal-point guides. Teacher mode makes the visuals bolder for projection.
- Press Calculate to refresh the answer, the whole-number layout, and the decimal-point explanation. Then use Back, Next, or Auto play.
Shortcuts: Alt+S share, Alt+L copy LaTeX, Alt+[ previous step, Alt+] next step.
Examples
Whole-number multiplication
Putting the decimal point back
Current explanation
Step list
Teacher notes
- Teach this page in two passes: the whole-number multiplication first, and the decimal-point step only after that part feels settled.
- Pause on the whole-number product before you count decimal places so students can see that the second phase is a separate decision.
- Use examples like 1.20 × 0.30 when you want to show that typed trailing 0s still matter while you decide where the decimal point goes back.
FAQ
Why can I ignore the decimal points first?
Because you can multiply the digits as whole numbers first, then put the decimal point back using the total number of decimal places.
How do I know where to put the decimal point back?
Count the decimal places in both inputs, add them, and move that many places from the right in the whole-number product.
Why does 0.03 × 0.02 need zeros on the left?
The whole-number product is 6, but you still need four decimal places in total, so the answer becomes 0.0006.
Why does 1.20 still count as two decimal places?
The typed zeros still show place value. They affect where the decimal point goes back, even if you later trim the final answer.
How can I check whether the answer is correct?
The panel under the result checks two different things: first the whole-number multiplication, then the decimal-place placement. If you keep trailing zeros in the display, the checking order stays the same even though the final formatting looks different.
Does this page work with negative numbers or fractions?
No. This first version is limited to whole numbers and decimals that are 0 or more.