Angles in degrees: what children learn
In this game children sort angles given in degrees into acute, right angle, obtuse and reflex. Knowing the boundaries, 90° and 180°, is all children need to sort any angle.
Supports part of Common Core 4.MD.C.5: angles measured in degrees. Reflex angles go a little beyond it. This focused game does not cover the entire standard.
Common Core connection: 4.MD.C.5. This is focused practice for part of the standard.
How to play
Sort the cards into the right groups. Tap a card, then its group. You can also drag a card, or press the number on its group. Each game has 3 rounds with no timer. Every card is checked as soon as you place it: a card in the wrong group comes back with a hint, and you get a point for each card you place right first time. For a quicker go, choose Quick quiz: 10 multiple-choice questions in 150 seconds (choose Relaxed for more time).
Step by step
- Acute: less than 90°. Any angle between 0° and 90° is acute.
- Right angle: exactly 90°. A quarter turn is 90°.
- Obtuse: between 90° and 180°. Wider than a right angle but less than a straight line.
- Reflex: between 180° and 360°. More than a half turn but less than a whole turn.
Worked examples
Example 1: 45°
Working: 45 is less than 90.
Answer: acute
Example 2: 135°
Working: 135 is between 90 and 180.
Answer: obtuse
Example 3: 270°
Working: 270 is between 180 and 360.
Answer: reflex
Common mistakes and how to fix them
- Calling 180° obtuse. 180° is a straight line. Obtuse angles are less than 180°.
- Forgetting reflex angles exist. Look at the outside of an angle: it is reflex if the inside is less than 180°.
- Reading the wrong scale on a protractor. Start from 0 on the arm of the angle and decide first whether the angle is acute or obtuse.
Activities to try at home
- Turn on the spot by 90°, 180°, 270° and 360°.
- Estimate angles in the house and check with a protractor.
- Find out how many degrees the minute hand turns in 15 minutes.
Ideas for the classroom
- Students estimate angles before measuring them with a protractor.
- Play 'angle bingo' with angles in degrees.
- Give a set of angles and ask students to order them and name each type.
Free printable game and worksheet
The free printable starts with a game sheet, such as a color-by-answer picture, an answer maze or a secret-code joke, followed by a worksheet. Both use the same checked questions as the online game, and the answers are on the last page. Print it, or save it as a PDF from your browser’s print menu.
Open the free printable game and worksheet
Frequently asked questions
How should I choose this game for my learner?
Supports part of Common Core 4.MD.C.5: angles measured in degrees. Reflex angles go a little beyond it. This focused game does not cover the entire standard.
Why are there 360 degrees in a whole turn?
It is a very old convention, probably from ancient Babylon. 360 divides by many numbers, which makes it useful.
Can it be played with a keyboard?
Yes. Tab to a card, press Enter to pick it up, then choose the group it belongs in.