How it works

There is no library of files here. Every sheet is built when you ask for it, from a small program that knows both the problem and how it is solved.

• 339 skills across 19 topics and 8 school years.
• 996 published sets — a skill is published once per difficulty band that is really different from the others, which is why 20 of them have two bands rather than three.
• 20 problems on a sheet, and a new sheet every time you ask.
• 347 different named mistakes the generators can recognise and explain.

Each generator builds the numbers first and the answer from the same numbers, so a sheet and its key cannot disagree. That is not enough on its own, so the build also re-derives the answers independently: a test reads the numbers off the rendered problem — the same ones you see — works the arithmetic out with its own code, and fails the build on any disagreement. It covers about two problems in five; the rest are held by named tests for fractions, money, percentages and the geometry formulas.

That test has already earned its place. It caught a subtraction whose two numbers were printed with different precision from the ones the answer used, so 8.82 − 1.20 appeared as 8.8 − 1.20 with the key still reading 7.62. Nobody would have noticed until a class did.

Every problem carries the specific wrong answers it invites, computed alongside the right one: the carry that never moved into the next column, the column subtracted smaller-from-larger, the numerators and denominators added separately, the divisor that was inverted instead of the dividend. When what you type is one of them, the page says which one happened rather than "incorrect" — and when you have the right value in the wrong form, it says that too, instead of marking you wrong.

It does not reproduce anybody's standards. Published standards are their authors' property under their own licence, so nothing on this site quotes one: every skill is named in our own words and every grade is our judgement, printed as ours. If a year looks wrong to you, it may well be.

It does not copy anybody's worksheets. Nothing here is scraped; there was nothing to scrape, because the problems are computed.

It is not a site for children to use unsupervised. It is a tool for the adult who sets the work — that is why there are no characters, no points and no badges.

It does not promise results. Practice is practice.

Press Copy assignment link and the set travels in the part of the address after the #. Everyone who opens it gets those exact twenty problems. That part of an address is never sent to a server, which is also why nothing you type on this site leaves your browser — see Privacy.