Understanding that angles on a straight line add up to 180° and using this to find missing angles.
Where your child meets this in real life: Calculating angles in construction, folding paper, or design
Each SEAG paper has 28 maths questions. Questions 29 to 50 are multiple choice with five possible answers, and questions 51 to 56 need a short written answer. With 56 questions in 60 minutes across English and maths, that is about a minute per question.
SEAGReady breaks angles on a straight line into 3 steps, taught in order so each skill builds on the last.
Find the missing angle when one angle on a straight line is given
Find a missing angle when two or more other angles on the same straight line are given
Identify which angles form a straight line in a diagram with intersecting lines, then calculate missing angles
Try three free questions from our angles on a straight line course. They start easy and get harder, so you can see where your child's confidence runs out. If they manage the last one without a hint, this topic is probably secure. If not, the steps above show where to start.
A ray divides the straight line shown. One angle is 70 degrees. What is the other angle?
On a straight line, there are three angles: 48 degrees, 67 degrees, and x degrees. Find the value of x.
Two lines cross at a point. One angle is 47 degrees. Another angle next to it is marked as x. A third angle, adjacent to x on the other line, is marked as y. Find the value of y.
This is the exact interactive worked example your child sees in SEAGReady. Step through it and watch the method build up.
Grace is measuring angles where a fence post meets a wall. One angle measures 65 degrees.
What is the other angle on the straight line?
180° − 65°
Angles on a straight line add up to 180°
Step 1 of 3
Grace is measuring angles where a fence post meets a wall. One angle measures 65 degrees.
What is the other angle on the straight line?
The other angle is 115° because angles on a straight line sum to 180°.
The key insight: A straight line is half a full turn, so the angles must add to 180°!
Common mix-up: 360° − 65° = 295°. That's for angles around a point. A straight line is only 180°.
These are the misconceptions we see most often in angles on a straight line, including the ones our practice questions are specifically designed to catch.
Struggling with angles on a straight line? The real gap is often in one of these earlier topics.
Sitting the SEAG test this November? Read our last-month revision plan, Paper 1 vs Paper 2 and test day guide.
SEAGReady finds the exact step where your child gets stuck, teaches it with worked examples like the one above, and brings it back for review so it sticks.
Free to start · no card needed