Finding a Missing Angle on a Straight Line
23 October 2026
Angle facts help children spot patterns and rules when working with shapes and lines. One of the most important rules is that angles on a straight line always add up to 180°. This is a key skill for the 11+ and is often tested in questions similar to the one below.
Find the missing angle x on a straight line if one angle is 70°
Angles on a straight line add up to 180°
Write the equation: 70° + x = 180°
Subtract 70° from both sides: x = 180° - 70°
x = 110°
The correct answer is 110°.
Angle chart
Straight line · 180°Key insight: Once your child knows this rule, they can quickly find a missing angle on a straight line by using simple subtraction. This type of question is common in 11+ maths.com uk practice, so it's useful to get familiar with the method. More practice questions like this are ready for your child to try next.
