An angle measures a turn, in degrees. Year 5 children name angles by their size and use two facts — a straight line is 180° and a triangle’s angles add up to 180° — to find missing angles.
What your child will learn
- Name acute, right, obtuse and reflex angles
- Know that angles on a straight line add up to 180°
- Know that the angles in a triangle add up to 180°
- Work out a missing angle
Four kinds of angle
An acute angle is less than 90°. A right angle is exactly 90°. An obtuse angle is between 90° and 180°. A reflex angle is more than 180°. If two angles sit on a straight line and one is 65°, the other must be 180 − 65 = 115°.
Example questions
Here are a few questions like the ones in the first quest. Can you solve them?
1. A right angle is split into two angles. One is 45°. What is the other, in degrees?
Show answer
Answer: 45. A right angle is 90°: 90 − 45 = 45.
2. An angle measures 100°. What kind of angle is it?
- Acute
- Right angle
- Obtuse
- Reflex
Show answer
Answer: Obtuse. It is between 90° and 180°, so it is obtuse.
3. An angle measures 330°. What kind of angle is it?
- Acute
- Right angle
- Obtuse
- Reflex
Show answer
Answer: Reflex. It is more than 180°, so it is reflex.
Tips for grown-ups
- Hunt for angles on a clock face: 3:00 is a right angle; 1:00 is acute.
- Tear the corners off a paper triangle and line them up — they make a straight line.