angles on a straight line
One angle on a straight line is 125°. Find the adjacent angle.
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The pattern behind it: Angle and shape properties
Mark the shape property first, then subtract known angles from the relevant total.
In this one. Use 180° only for adjacent angles whose outside arms form a straight line.
How to spot it
Look for a named quadrilateral like a rhombus or parallelogram, plus two straight lines crossing inside or through it. Words like "straight line" and "collinear" point to this move.
Common mistake
Children mix up which angle sits opposite which once lines cross at a point away from the main shape. Trace each ray back to its two labelled ends before deciding what faces what.
Try one like it
Standard angles around a point Three angles around a point are 85°, 65° and 120°. Find the remaining angle.The 33 problem patterns
All 33 patterns, one to a page — the 19 behind Primary 5 and 6 word problems, and the skills the younger years are built on. The bar model, how to spot it in the question, and the mistake children make. A booklet you can print. Free.
A PDF, and a note when new solutions go up.