Triangles & Quadrilaterals questions for Primary 5 Maths

Every answer with the reasoning behind it. Worth reading after you have tried the set — or on its own, if you are a parent marking it.

1. Two angles of a triangle are 55° and 65°. What is the third angle?

   Answer: 60°

   The angles of a triangle add to 180°: 180 − 55 − 65 = 60°.

2. An isosceles triangle has a top angle of 40°. What is each of its two base angles?

   Answer: 70°

   180 − 40 = 140° shared between two equal base angles, so 140 ÷ 2 = 70°.

3. Three angles of a quadrilateral are 110°, 75° and 95°. What is the fourth angle?

   Answer: 80°

   110 + 75 + 95 = 280, and 360 − 280 = 80°.

4. Which statement about a rhombus is TRUE?

   Answer: All four sides are equal

   A rhombus has four equal sides; its angles are equal only in opposite pairs.

5. What is the size of each angle in an equilateral triangle?

   Answer: 60°

   180 ÷ 3 = 60°, since all three angles are equal.

6. One angle of a parallelogram is 65°. What is the angle next to it?

   Answer: 115°

   Angles next to each other in a parallelogram add to 180°: 180 − 65 = 115°.

7. A four-sided shape has exactly one pair of parallel sides. What is it?

   Answer: Trapezium

   A trapezium is the quadrilateral with exactly one pair of parallel sides.

8. One angle of a right-angled triangle is 35°, not counting the right angle. What is the third angle?

   Answer: 55°

   180 − 90 − 35 = 55°.

9. Which shape always has four equal sides AND four right angles?

   Answer: Square

   Only a square is guaranteed both four equal sides and four right angles.

10. The angles of a triangle are in the ratio 1 : 2 : 3. What is the largest angle?

    Answer: 90°

    1 + 2 + 3 = 6 units for 180°, so 1 unit is 30° and the largest is 3 × 30 = 90°.