Angles

Advanced Math 4 · Unit 15 · angle-measure-types · Teacher edition

angle-measure-types

Name ______________________________Date ______________

1.
An angle measures $115^\circ$ . Which word describes it?
1. (A)
  acute
2. (B)
  right
3. (C)
  obtuse
4. (D)
  straight
2.
Three angles meet at a point and together fill the whole turn around it. Two of the angles are $150^\circ$ and $95^\circ$ . What is the third angle, in degrees?
Answer: ______________
3.
Priya measures an angle with a protractor. One ray of the angle lies along the $0^\circ$ mark of the inner scale. The other ray crosses the protractor where the inner scale reads $40^\circ$ and the outer scale reads $140^\circ$ . The angle is smaller than a right angle. What is its measure?
1. (A)
  $140^\circ$
2. (B)
  $40^\circ$
3. (C)
  $50^\circ$
4. (D)
  $320^\circ$

Answer key — Angles

1.
(C)
obtuse
angle-measure-types-01
$115^\circ$ is more than $90^\circ$ and less than $180^\circ$ , so it is obtuse. (Acute is under $90^\circ$ ; right is exactly $90^\circ$ ; straight is exactly $180^\circ$ .)
2.
115angle-measure-types-02
$360 - (150 + 95) = 360 - 245 = \mathbf{115}$ degrees. (Using $180$ instead of $360$ would give a negative number, a sign that the wrong total was used.)
3.
(B)
$40^\circ$
angle-measure-types-03
The first ray is on $0^\circ$ of the inner scale, so the inner reading is the measure: $\mathbf{40^\circ}$ . It is acute, as the prompt says. ( $140^\circ$ reads the wrong scale and would be obtuse; $50^\circ$ is $90 - 40$ , a misread; $320^\circ$ is the reflex angle on the outside.)