Fraction Addition & Subtraction
Practice fraction addition and subtraction with a free, browser-based math game. Includes step-by-step strategy, common mistakes, and classroom tips.
MathAngles & Missing Degrees
Complementary angles add to 90°, supplementary angles add to 180°, and the three interior angles of a triangle always add to 180°. Below: the three relationships and how to use them under time pressure.
Choose your difficulty
Pick a level to start playing. You can switch at any time.
How to play
Work out the missing angle, then tap the correct value.
Tip: your progress and best score are saved in this browser only.
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MathWhat you are actually practicing
Angles are one of the few topics in basic math where the answer is not computed by a rule you apply, but by a relationship you have to recognise first. Two angles that add to 90 degrees are complementary. Two that add to 180 are supplementary. The three interior angles of any triangle always add to 180. Once you see which relationship is on screen, the arithmetic left is one subtraction.
This game drills exactly that: recognise the relationship, then find the missing angle.
How the game works
You are shown an angle expression with one value missing, and four possible answers. Pick the right one before the countdown ends. Get it wrong and the correct value is revealed immediately, so a miss costs you a point but teaches you the pair.
Easy is complementary angles only. Medium adds supplementary angles. Hard adds triangles, where two angles are given and you must find the third.
The relationships worth knowing
Complementary: the pair adds to 90°. If one is 35°, the other is 90° - 35° = 55°.
Supplementary: the pair adds to 180°. If one is 112°, the other is 68°.
Triangle interior angles: all three add to 180°. Given 47° and 68°, the third is 180° - 47° - 68° = 65°.
Strategies that actually raise your score
Read the big number as a clue. If you see 90, you are subtracting from 90. If you see 180, you are subtracting from 180. The large number is always the total, never one of the parts.
Use the last digit when time is short. For 90 - 35 the answer must end in 5. For 180 - 47 it must end in 3. Narrowing the options to the matching one takes two seconds and works every time.
In triangle questions, add the two given angles first. 47 + 68 = 115, then 180 - 115 = 65. Doing it in a single step invites arithmetic slips under the countdown.
Sanity-check the size. A missing angle in a triangle is always below 180°, and if both given angles are large it must be small. If your answer is bigger than the total, you subtracted backwards.