IMC 2007 Q7
7. If the numbers 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 are all multiplied together, how many zeros are at the end of the answer?
- A 1
- B 2
- C 3
- D 4
- E 10
Intermediate Mathematical Challenge 2007, Question 7. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: B 2
The product = 1 × 3 × 4 × 6 × 7 × 8 × 9 × (2 × 5) × 10. The product of the first seven of these numbers is not a multiple of 10, so the original product is a multiple of 100, but not a multiple of 1000.
Solution © UK Mathematics Trust, from the IMC 2007 solutions.