How to use this sheet

  • Have the child decide whether each angle is acute, right or obtuse before measuring it. The measurement should agree.
  • Show how to line up the protractor: the small mark in the middle of the straight edge on the vertex, and the zero line on one arm.
  • For missing angles, have the child write the equation, such as 90 − 35, before working it out.

Common mistakes

  • Reading the wrong scale on the protractor, so a 40 degree angle is read as 140. Check: is the angle acute or obtuse?
  • Thinking an angle with longer arms is bigger. Only the turn between the arms matters.
  • Placing the corner or the edge of the protractor on the vertex, instead of the mark in the middle of its straight edge.

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