At the end of any kind of test, it’s important to check your work. Checking in English is relatively easy because you just have to look out for mistakes with spelling, capital letters, punctuation or other grammar. However, checking in Maths is much harder because there are so many different types of questions. So what’s the answer?

Well, you could always repeat your working for every single question, but that means any test would take twice as long! You don’t have time to do that, so there must be another way. In my experience, you should learn a few different ways of checking that are simple and quick to use.

If you have a mental checklist to go through, it should help you avoid silly mistakes.

# Instructions

Have you read all the instructions on the front page? They might contain important guidelines about how to do the exam. For example, you might be told to show your working for every sum—even if there’s no mark scheme, which would usually mean there’s just one mark for a correct answer.

# Units

The easiest and quickest way to check your answer is to make sure you’ve included the units! It may be true that 25 x £1.60 is £40, but you won’t get the mark unless you put in the pound sign…

# Numbers

Have you copied down the numbers correctly in your sums? You’ll never get the right answer if you’re asking the wrong question…!

# Multiplication

There are a couple of ways of checking a multiplication sum.

## Last Digits

1. Multiply the last digits of both numbers together.
2. Make sure the last digits of that number and your answer are the same.
• Eg 3,792 x 26 must end with a 2 because 2 x 6 = 12, and 12 ends with a 2

# Rounding

1. Round both numbers to one (or two) significant figures.
2. Multiply them together.
3. Make sure the number you get and your answer are roughly the same size.
• Eg 3,792 x 26 must be roughly 120,000 because 4,000 x 30 = 120,000

# Geometry

Sometimes, drawing a diagram of a problem can help you check your answer. For example, if two angles of an isosceles triangle are both 20° and you need to find the other, you can make a rough drawing of the triangle and check to see if your answer is likely.

If you can’t remember if the internal angles of a triangle add up to 90°, 180° or 360°, say, your diagram will tell you that the missing angle has to be obtuse (between 90° and180°). That means it must be 140° (180° – 2 x 20°), not 50° (90° – 2 x 20°) or 320° (360° – 2 x 20°).

Angles around a point add up to 360º.

• Eg if two of the angles are 45° and 30°, the other one must be 360° – (45° + 30°) = 360° – 75° = 285°.

Angles on a straight line add up to 180º.

• Eg if two of the angles are 45° and 30°, the other one must be 180° – (45° + 30°) = 180° – 75° = 105°.

Alternate angles are equal, ie the angles under the arms of a ‘Z’ formed by a line (or ‘transversal’) bisecting two parallel lines.

• Eg if one of the angles is 45°, the other one must also be 45°.

Corresponding angles are equal, ie the angles under the arms of an ‘F’ formed by a line (or ‘transversal’) bisecting two parallel lines.

• Eg if one of the angles is 45°, the other one must also be 45°.

Complementary angles add up to 90º, ie any angles that combine to form a right angle.

• Eg if two of the angles are 45° and 30°, the other one must be 90° – (45° + 30°) = 90° – 75° = 15°.

The internal (or interior) angles of a triangle always add up to 180°.

• Eg if two of the internal angles are 45° and 30°, the other one must be 180° – (45° + 30°) = 180° – 75° = 105°.

All three sides and all three angles are equal in an equilateral triangle.

• Eg if one side is 3 cm long, the other sides will also be 3 cm long. The internal angles of any triangle add up to 180°, so all three angles must be 180° ÷ 3 = 60°.

Two sides and two angles are equal in an isosceles triangle.

• Eg if one of the two equal sides is 3 cm long, the other one will also be 3 cm long. If one of the equal angles is 30°, the other one will also be 30°. If the ‘odd’ angle is 30°, the other two must both be (180° – 30°) ÷ 2 = 75°.

No sides and no angles are equal in a scalene triangle.

• Eg if one side is 3 cm long, no other side can be 3 cm long. If one angle is 30°, no other angle can be 30°.

The internal (or interior) angles of a quadrilateral add up to 360°.

• Eg if two of the internal angles are 45° and another one is 135°, the other one must be 360° – (45° x 2 + 135°) = 360° – 225° = 135°.