IMC 2007 Q11
11. The numbers 72, 8, 24, 10, 5, 45, 36, 15 are grouped in pairs so that the product of each pair is the same. Which number is paired with 10?
- A 36
- B 45
- C 24
- D 15
- E 72
Intermediate Mathematical Challenge 2007, Question 11. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: A 36
As the product of each pair has the same value, this value must be product of the smallest and largest numbers, that is 5 × 72. So the number which is paired with 10 is (5 × 72) ÷ 10, that is 36.
Solution © UK Mathematics Trust, from the IMC 2007 solutions.