Measuring Angles Using a Protractor

Do you agree that ∠a = 90°.

• Yes. The top line of the angle is aligned to 90°.

• No. The measurement is not accurate because the bottom line of the angle is not aligned to the baseline of the protractor.

Do you think this is a 85° angle?

• Yes

• No

Is this the correct way of using a protractor to measure an angle

• Yes

• No

Why is this not a 85° angle?

• 85° is an acute angle. The picture shows a right angle as it is 90°.

• 85° is an obtuse angle. The picture shows an acute angle as it is less than 90°.

• 85° is an obtuse angle.The picture shows an acute angle as it is less than 90°.

• 85° is an acute angle. This picture shows an obtuse angle as it is more than 90°.

Is this the correct way of using a protractor to measure angles?

• Yes

• No

∠a = ______°

• 75

• 85

• 105

• 115

We will read the measurement from the __________ scale.

• inner

• outer

We should read the measurement based on the inner scale because '0' starts from the ______.

• inner scale

• outer scale

∠DEF = ______°

• 34°

• °146

This is the wrong way of using a protractor because __________.

• the bottom line of the angle is not aligned to the baseline of the protractor.

• the vertex of the angle is not aligned to the centre of the protractor.