How questions and solutions are checked

Where the questions come from

Every question is labelled with where it came from, so you always know what you are looking at:

• Past paper and adapted: from Lancaster exams and class tests, or reworked from one where only part is still taught.
• Exercise and tutorial: from the module's problem sheets and the worked examples in the lecture slides.
• Lecture: questions the lecturer poses in the slides. Drill: short formula practice. Generated: new questions written for the site in the same style as the papers.

The current lecture slides decide what is on the syllabus. Before a past paper question is used, it is checked against them and marked as fully covered, partly covered (then adapted), no longer taught (then left out), or unclear. Papers from the modules these ones replaced are marked Old spec.

How a solution is written

• From first principles: assumptions, sign convention and the governing equations come before any numbers.
• Only the methods and notation from the current slides. Anything from outside the course is labelled as such.
• Units carried through every step, and data the question does not print (for example from a data book) stated where it is used.
• All arithmetic is done in code, not by hand or in someone's head. Steam and water properties come from the IAPWS-97 formulation and are quoted to table precision.
• Drafting is AI-assisted, under a written accuracy protocol; the checks below apply to every solution however it was drafted.

How it is checked

Each numerical part is checked in at least two independent ways, chosen from:

• solving it a second way (a different method or route);
• checking units at every step;
• a limiting case or a rough size check (is the answer physically sensible?);
• putting the answer back into the original equations.

Where official solutions or numerical answers exist, the question is solved independently first and then compared. Official answers can be wrong too. When the two disagree, both are re-checked and the solution note says which one is trusted and why.

Confidence ratings

Every worked solution shows a confidence rating:

• High: the methods agree and every check passed.
• Medium: one of the checks could not be done (for example a value read off a chart, or no official answer to compare with), or a small question remains. The solution says what to confirm with a lecturer or classmate.
• Low: the question is ambiguous or sources disagree. The solution states the assumption it made. Treat it with care.

Right now 413 questions have worked solutions: 377 rated high, 36 medium and 0 low. These numbers update whenever questions are added.

What "[Added]" means

Some lecture questions are derivations or "show that" tasks with no numbers. To give you something you can check, a few have extra values added, marked [Added] in the question. Those values are not from the lecturer; they only turn the derivation into a calculation with a final answer you can test yourself on.

Checking your own answer

Where a question has a numerical answer, the answer box accepts anything within 2% of the worked value, or 5% where the method involves reading a chart or table, so rounding differences are not marked wrong.

Found a mistake?

Every question has a Report a mistake button under the solution. Say what looks wrong and, if you can, the answer you got. The report goes straight to the site owner with the question attached; your email is optional and only used to reply.

The aim is to read every report within a few days and to put a confirmed error right in the next update, usually within a week. If a report shows a solution is wrong, it is corrected and re-checked in the same way as a new one. Fixes and new content are listed on What's new.

What this does not mean

None of this makes the solutions official. They are not checked by lecturers, and the slides, the lecturer and published mark schemes always come first. See academic integrity for what the solutions are for.