Math · Stage 4

Reason about angles (on a line, vertically opposite, in triangles)

Three facts unlock almost every angle puzzle: angles on a straight line add to 180°, vertically opposite angles are equal, and the angles inside a triangle add to 180°.

✦ Math📘 Stage 4 · S4⏱ ~12 min🧒 Ages 8–9★ Free to start

I can reason about angles (on a line, vertically opposite, in triangles).

Start the free lesson →⬇ Printable PDF

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Kavi the Angle Detective 🔎

A puzzle shows an angle with a missing number! "I don't need a protractor," hoots Kavi. "I just need three facts: angles on a straight line add to 180°, angles that cross are vertically opposite and equal, and the three angles inside a triangle add to 180°. With those, I can reason out any missing angle! 🔎"

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What your child will learn

1On a straight line → add to 180°

2When two lines cross: opposite angles matchWhen two straight lines cross they make an X with four angles. Tap each card to see the pattern.

3Angles in a triangle add to 180°The three angles inside any triangle always add up to 180°. To find a missing angle, add the two you know, then take that from 180°. Here the known angles are 60° and 70° — tap Step → to add them first.

4Two different 180°s180° shows up twice — but with a different number of angles. Tap each card so you know which to use.

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A peek inside

Two angles sit together on a straight line. One of them is 130°. What is the other angle?

angles on a line add to 180° → 180 − 130

Try this at home: Angles on a straight line add to 180°. One angle is 110°, so the other is 180 − 110 = __

Ready to play and learn?

Start the free interactive lesson, or print the handout for screen-free play.

Start the free lesson →⬇ Download PDF

Part of Math · Stage 4 · S4 on KAVI Academy — a secular, whole-child learning platform for ages 5–12.