MathGrade 5ages 10–11
📐 Angle sum
A child who is more familiar with a full 360-degree turn may guess that a triangle's three angles add up to 360, because a full turn is the round number they know best.
Try this lesson freeNo card needed. The first lesson is free.
Download on the App StoreWhat your child learns
- In every triangle, the three angles together are 180 degrees.
- That is a half turn, which is a straight line.
- The rule holds for every triangle, big or small, wide or narrow.
- If two angles are known, the third is whatever is left up to 180.
The mistake most kids make here
Confusing a half turn with a whole turn.
Try one question
Angles of 60, 70 and 50. What do they add up to?
60 + 70 + 50
- 180
- 360
- 120
Answer
180 — Yes. And that is the total for every triangle.
How Maya teaches it
Your child tells Maya what they did in class. She teaches this topic at her desk, asks questions with tappable answers, and when the answer is wrong she explains why that answer was tempting instead of saying “try again”. She remembers what did not land and comes back to it.
Your child has it when they can: What do the three angles close to, and how do you find the third?
How to help at home
This mix-up is not about the arithmetic — it is about which turn the child pictures. A straight line is a half turn, 180 degrees, and that is the total the three angles of any triangle share.
Draw a triangle on paper and tear off its three corners. Line the three torn corners up edge to edge on a table, and they will form a straight line — a visible half turn, not a full circle.
Try this with two very different triangles — one tall and thin, one short and wide — so your child sees the same straight-line result happen every time, no matter the triangle's shape.
A sign they have it: given two of a triangle's three angles, they subtract from 180 to find the third, and can explain why 180 and not 360 is the total.
Questions parents ask
- Why does my child think a triangle's angles add up to 360?
- 360 degrees is the full-turn number children usually meet first, so it can get applied to any shape's angles without checking whether the shape actually makes a full turn.
- What is a hands-on way to show the angle sum of a triangle?
- Tear the three corners off a paper triangle and line them up edge to edge — they will form a straight line, which is a half turn of 180 degrees.
- Does the 180-degree rule work for every triangle?
- Yes — it holds for every triangle regardless of its shape or size, which is why testing it on two very different triangles is convincing.
- How does Maya teach the angle sum of a triangle?
- Maya has the child compare the torn-corner result on two different-shaped triangles, so 180 degrees is seen as a rule about all triangles, not one example.
No card needed. The first lesson is free.
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