IMC 2008 Q2
2. Which is the largest prime number that divides exactly into the number equal to 2 + 3 + 5 × 7 ?
- A 2
- B 3
- C 5
- D 7
- E 11
Intermediate Mathematical Challenge 2008, Question 2. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: C 5
2 + 3 + 5 × 7 = 5 + 35 = 40. As 40 = 23 × 5, the largest prime number which divides exactly into it is 5.
Solution © UK Mathematics Trust, from the IMC 2008 solutions.