Angles · Grade 6
In Grade 6 you learn: angle notation.
An angle measures an amount of turn. We measure angles in degrees with a protractor and sort them by size: acute, right, obtuse, straight and reflex.
Key facts
- Acute: less than 90°. Right angle: exactly 90°. Obtuse: between 90° and 180°.
- Straight angle: exactly 180°. Reflex: between 180° and 360°.
- A full turn is 360°.
- On a clock, each hour gap is 30°; the minute hand turns 6° per minute and the hour hand 0.5° per minute.
Worked examples
Example 1
The marked angle is 130°. Is it acute, obtuse or reflex? What is the reflex angle on the other side?
Answer: Obtuse; the reflex angle is 230°.
Example 2
What is the smaller angle between the hands of a clock at 4 o’clock?
Answer: 120°
Example 3
What is the smaller angle between the hands of a clock at 2:30?
Answer: 105°