Types of angle and measuring for the 11 plus

Acute is less than 90 degrees. A right angle is exactly 90. Obtuse is between 90 and 180. Straight is 180. Reflex is more than 180. To measure: put the middle of the protractor on the corner, line one arm up with zero, and read the scale that starts at zero on that arm.

Guess first. Is it acute or obtuse? This one is acute, so the answer is under 90. The scale that begins at 0 on our arm reads 50.

The trap is reading the wrong scale and writing 130. The two numbers add to 180. Your first guess says which one is possible.

Part of the Geometry topics for the 11+.

• 6.1Properties of 2D shapesFold it in your head before you count
• 6.2Perimeter and missing lengthsPerimeter is a walk, not a space
• 6.3AreaUse the height that stands up straight
• 6.43D shapesCount the edges you cannot see
• 6.5Volume and capacityVolume means multiply, never add
• 6.7Angle factsKnow the total, find what is left
• 6.8Position and coordinatesAlong the corridor, then up the stairs

Every 11 plus maths topic