Triangles & Quadrilaterals questions for Primary 6 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 47° and 68°. What is the third angle?

   Answer: 65°

   The three angles of a triangle add to 180°, so 180 − 47 − 68 = 65°.

2. Three angles of a quadrilateral are 80°, 95° and 110°. What is the fourth angle?

   Answer: 75°

   The four angles of a quadrilateral add to 360°, so 360 − 285 = 75°.

3. Each interior angle of a regular hexagon is 120°. What is the sum of its interior angles?

   Answer: 720°

   A hexagon has 6 interior angles, and 6 × 120° = 720°.

4. A quadrilateral has all four sides equal and no right angles. What is it?

   Answer: Rhombus

   Four equal sides without right angles describes a rhombus.

5. Which statement about a parallelogram is always true?

   Answer: Opposite sides are equal and parallel

   A parallelogram has two pairs of opposite sides that are equal and parallel.

6. An isosceles triangle has a vertex angle of 40°. What is each base angle?

   Answer: 70°

   The two base angles share 180° − 40° = 140°, so each is 70°.

7. A regular polygon has interior angles that add to 1080°. How many sides does it have?

   Answer: 8

   Sum = (n − 2) × 180°. 1080 ÷ 180 = 6, so n − 2 = 6 and n = 8. It is an octagon.

8. A straight line from the centre of a circle to a point on the circumference is called the

   Answer: radius

   The radius joins the centre to the circumference. Two radii make a diameter.

9. A right-angled triangle has an acute angle of 35°. What is the other acute angle?

   Answer: 55°

   The two acute angles of a right-angled triangle add to 90°, so 90 − 35 = 55°.

10. Which of these shapes is NOT a parallelogram?

    Answer: Trapezium

    A trapezium has only one pair of parallel sides, so it is not a parallelogram.