Angle Sum Rules · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Angles that add up

Mathematics · Geometry · ages 9-10
Name ______________________   Date ____________

  1. An angle on a straight line measures 65 degrees. What does the angle next to it measure?

    Answer: ______________

  2. Two angles sit side by side on a straight line. One angle measures 110 degrees. How big is the other angle?

    • 70 degrees
    • 80 degrees
    • 90 degrees
    • 110 degrees

  3. Two angles sit on a straight line. What do they always add up to?

    • 180°
    • 90°
    • 360°

  4. Four right angles fit exactly around one point.

    Circle one:   True   False

  5. Three angles meet at one point. They measure 90 degrees, 120 degrees, and x degrees. Find x.

    Answer: ______________

  6. Four angles meet at a point: 100°, 80°, 90°, and one more. What is the missing angle?

    Answer: ______________

  7. How many right angles do you need to put together to make 270 degrees?

    • 2
    • 3
    • 4
    • 5

  8. Two angles sit together on a straight line. One of them measures 135 degrees. What is the other one?

    Answer: ______________

  9. Which pair of angles could sit side by side on a straight line?

    • 45 degrees and 45 degrees
    • 60 degrees and 120 degrees
    • 100 degrees and 90 degrees
    • 30 degrees and 140 degrees

  10. Milo says 130° and 60° are two angles on a straight line. Is that possible?

    • Yes, they add to 180°
    • No, they add to 190° not 180°
    • No, they add to 170° not 180°
LightMySky · lightmysky.comW1-mt_oqziWKry-L-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Angles that add up W1-mt_oqziWKry-L-s1

  1. 115 · The two angles on a straight line add to 180 degrees, so the missing angle is 115 degrees.
  2. 70 degrees · Angles on a straight line add up to 180 degrees, so the missing angle is 70 degrees.
  3. 180° · A straight line is half a turn, so angles on it add up to 180°.
  4. True · Each right angle is 90°, and 90° + 90° + 90° + 90° = 360°.
  5. 150 · Angles around a point add up to 360 degrees, so x is 150 degrees.
  6. 90 · Add the known angles first: 100° + 80° + 90° = 270°. Then 360° − 270° = 90°.
  7. 3 · Each right angle is 90 degrees, and 270 divided by 90 is 3.
  8. 45 · The angles on a straight line add to 180 degrees, so the missing angle is 45 degrees.
  9. 60 degrees and 120 degrees · Only 60 and 120 add up to 180 degrees, the rule for a straight line.
  10. No, they add to 190° not 180° · 130° + 60° = 190°, which is too much for a straight line.
Worksheet · LightMySky