Correctly finds ∠QRS = 112° but then sets ∠RSP = 112° (same as ∠QRS). ∠RSP is opposite ∠PQR, so ∠RSP = 68°. The pattern alternates: 68°, 112°, 68°, 112°.
PRIMARY 6 · MATHEMATICS
Geometry
Top 5 mistakes
Ranked by how often they appear across 22 MOE-aligned practice questions in our archive.
This incorrectly makes ∠QRS equal to ∠PQR (68°). Adjacent angles in a rhombus are supplementary, not equal: ∠QRS = 180° − 68° = 112°. Only opposite angles are equal.
Gives three angles of 112°: 68° + 112° + 112° + 112° = 404°, which exceeds 360°. Interior angles of any quadrilateral must sum to exactly 360°.
Computed angle ADC = 180° - 110° = 70° (correct co-interior angle on side AD) but reported that as angle BCD instead of working out the OTHER pair on side BC.
Used 360° - 110° - 60° - 90° = 100°, treating the trapezium as having one right angle at C.
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