Angles and Angle Measurement — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. A triangle has two 45° angles. What type of triangle is it?
A) Equilateral
B) Obtuse
C) Right
D) Straight
Two 45° angles sum to 90°, so the third angle = 180 − 90 = 90°. A 90° angle makes it a right triangle.
2. What is the sum of all angles in a rectangle?
A) 180°
B) 270°
C) 360°
D) 400°
A rectangle has four 90° angles: 4 × 90° = 360°.
3. What angle do the hands of a clock make at 3:00?
A) 60°
B) 90°
C) 120°
D) 180°
At 3:00, the minute hand points to 12 and the hour hand points to 3 — they are perpendicular, forming a 90° angle.
4. Each angle of an equilateral triangle measures how many degrees?
A) 45°
B) 60°
C) 90°
D) 120°
An equilateral triangle has three equal angles summing to 180°: 180 ÷ 3 = 60° each.
Part B: Fill in the Blank
Write the correct answer on each line.
1. The sum of all angles in any triangle is 180 degrees.
The Triangle Angle Sum theorem states that all three interior angles always sum to 180°.
2. A quadrilateral has angle measures 80°, 100°, and 90°. The missing angle is 90 degrees.
360 − 80 − 100 − 90 = 90°.
3. At 6:00 the clock hands form a straight angle.
At 6:00 both hands point in opposite directions along a straight line, forming a 180° straight angle.
4. A triangle with one angle of 120° is called an obtuse triangle.
A triangle with one angle greater than 90° is an obtuse triangle.
5. If two angles of a triangle are 35° and 55°, the third angle is 90 degrees.
180 − 35 − 55 = 90°, making it a right triangle.