geometry · Year 5 · AC9M5M04

Using a protractor

Put the centre of the protractor on the corner of the angle and line the baseline up with one arm. That arm points to 0 on one of the two scales. Follow that same scale round to the other arm and read the number. Then check: if the angle is smaller than a right angle, the answer must be less than 90. If neither arm is on 0, read both arms on the same scale and find the gap between the numbers.

Sample questions

Use the protractor. How many degrees is the marked angle?

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  1. The arm along the baseline points to 0 on the inner scale, so read the inner scale.
  2. The angle is smaller than a right angle, so the answer must be less than 90.
  3. The other arm points to 50 on the inner scale, so the angle is 50°.

Answer: 50

Use the protractor. How many degrees is the marked angle?

18001701016020150301404013050120601107010080909080100701106012050130401403015020160101700180
  1. The arm along the baseline points to 0 on the inner scale, so read the inner scale.
  2. The angle is bigger than a right angle, so the answer must be more than 90.
  3. The other arm points to 130 on the inner scale, so the angle is 130°.

Answer: 130

Use the protractor. How many degrees is the marked angle?

18001701016020150301404013050120601107010080909080100701106012050130401403015020160101700180
  1. The arm along the baseline points to 0 on the inner scale, so read the inner scale.
  2. The angle is smaller than a right angle, so the answer must be less than 90.
  3. The other arm points to 80 on the inner scale, so the angle is 80°.

Answer: 80

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