Working Rules

A science lab has safety rules. A maths lab has working rules. They keep your answers honest.

• Show your steps. A correct answer with no steps cannot be checked, and a wrong answer with steps can be fixed.
• Check the units. 50 g and 50 kg are very different; so are 30° and 30 cm. Write the unit on every answer.
• Estimate before you calculate. If 0.3 × 0.4 must be less than 0.3, then 1.2 cannot be right.
• A wrong answer is information. It tells you which idea to look at again. Read “what you should have done” carefully.
• Never rub out your working. Cross it out with one line, so you can see later what you tried.
• Check by going backwards. Put your answer back into the equation; check a subtraction by adding.
• Test a rule before you trust it. One counter-example is enough to break a rule. A few examples are never enough to prove one.