The idea in brief. An angle has one vertex and two arms, and both of the things this node asks follow from finding it. To NAME the angle, put the vertex letter in the middle. To MEASURE it, put the protractor's centre mark on the vertex and its base line along one arm, then read the scale whose zero is on that arm.
Lesson video, with the working
Naming and measuring angles
4 min 15 s
The film teaches 2 questions in turn. Each question shows first; its working is written as the film explains it.
The vertex letter goes in the middle, with one point from each arm on either side of it.
∠x = ∠LNP = ∠PNL
Answer: ∠x = ∠LNP = ∠PNL
For parents
How can I help my child with naming and measuring angles?
An angle has a name as well as a size, and your child needs both to describe exactly which opening a question means.
What your child learns here
An angle has a name as well as a size, and your child needs both to describe exactly which opening a question means. The Primary 4 syllabus introduces notation such as ∠ABC and measurement in degrees. This page connects the letters on a figure to the centre and baseline of a protractor, so the measurement belongs to the intended angle even when its arms are tilted.
Locate the vertex where the two arms meet, and put its letter in the middle when naming an angle with three letters.
Read the angle symbol and a small-letter name such as ∠a without treating either as a side length.
Place the protractor's centre on the vertex, align its baseline with one arm, and read from the zero on that arm.
Describe the opening in degrees, using a right angle as a reference for whether the measurement should be below or above 90°.
Does the answer make sense?
If the marked opening is smaller than a right angle, its measurement must be less than 90°. A reading above 90° for that same opening tells your child to check which zero starts the protractor scale before accepting the number.
How to practise these questions
The Basic questions focus on naming an angle in different ways and deciding whether a name identifies the intended opening. Intermediate work includes choosing a protractor scale, extending a short arm and measuring turns in a path or a moving object. Challenge questions compare measured openings and ask for the greatest angle or both the greatest and smallest named angles. Work on the naming questions first if locating the vertex is still uncertain, then ask your child to explain the starting zero before taking a reading. For the turn questions, identify the directions of travel or movement carefully. After checking the working, revisit the part that needed help rather than repeating a measurement without understanding its alignment. Its multiple-choice Basic questions read an angle from a drawn protractor, which means choosing the scale that starts at 0 on the angle's arm, or pick the three-letter name of a marked angle.
Questions parents ask
Why is the middle letter in an angle name so important? It identifies the vertex, the point where the two arms meet. In ∠ABC, the opening is at B and the arms go towards A and C. Your child can name the same opening ∠CBA, but moving B out of the middle can name a different angle. Ask your child to touch the vertex before reading the three letters aloud.
Which of the two protractor scales should my child use? Use the scale whose zero lies on the arm chosen as the starting line. The other arm then meets the required reading on that same scale. A protractor has two scales so either direction can be measured; the smaller printed number is not automatically the answer. A quick comparison with a right angle helps your child choose sensibly.
Does a longer arm make an angle larger? Extending an arm in the same direction leaves the angle unchanged. Angle size describes the opening between the directions, rather than the amount of ink used to draw them. A short arm may need extending with a ruler to reach the protractor scale, but your child should keep that extension on the original straight line.
