How to Check Calculation Working Before You Submit an Answer

Many lost marks in maths and science come from calculations where the arithmetic was fine but the set-up was not. The answer looks reasonable, so it never gets checked. A short routine, used every time, catches most of these before they cost you.

Before you calculate

• Write what you are finding, with its unit.
• List the given values, each with its unit.
• Write the relationship you will use in symbols before substituting numbers.
• Note anything already present at the start, such as an initial amount or a starting value.

That last point matters. A common error is calculating as if a quantity starts from zero when the question says it does not. The arithmetic can be perfect and the answer still wrong.

After you calculate

1. Estimate. Round the numbers and ask whether your answer is about the right size.
2. Substitute back. Put your answer into the original relationship and see if it holds.
3. Check units. Does the unit of your answer match what was asked?
4. Check precision. Follow the question's instruction on decimal places or significant figures.

Log what the check catches

When a check catches an error, write down which step failed. Over a few papers you will see whether your problem is set-up, units or rounding, and you can practise that directly.

Australian Study Resources has a worked example of this routine, including how a plausible wrong answer arises, in how to check calculation working before submitting an answer. It is a separate free site, published by the same company that operates ATARMAxxing.

Subject-specific practice

Our HSC Chemistry guide to fixing calculation errors and WACE Chemistry guide to checking your working apply the same idea to stoichiometry and concentration questions. For maths, see checking your method in VCE General Maths. Then practise under exam conditions with papers from the past papers index.