IMC 2011 Q5
5. The diagram shows a rectangle placed on a grid of 1 cm × 1 cm squares.
What is the area of the rectangle in cm2?
- A 15
- B \(22\frac{1}{2}\)
- C 30
- D 36
- E 45
Intermediate Mathematical Challenge 2011, Question 5. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: C 30
Triangles \(A\) and \(C\) are each of area \(\tfrac{1}{2}\) × 5 × 5 cm2.
Triangles \(B\) and \(D\) are each of area \(\tfrac{1}{2}\) × 3 × 3 cm2.
So the shaded area is [64 − (25 + 9)] cm2 = 30 cm2.
Solution © UK Mathematics Trust, from the IMC 2011 solutions. Longer versions with investigations: Solutions and investigations (PDF).