IMC 2012 Q9
9. Auntie Fi's dog Itchy has a million fleas. His anti-flea shampoo claims to leave no more than 1% of the original number of fleas after use. What is the least number of fleas that will be eradicated by the treatment?
- A 900 000
- B 990 000
- C 999 000
- D 999 990
- E 999 999
Intermediate Mathematical Challenge 2012, Question 9. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: B 990 000
1% of 1 000 000 = 1 000 000 ÷ 100 = 10 000. So the least number of fleas which will be eradicated is 1 000 000 − 10 000 = 990 000.
Solution © UK Mathematics Trust, from the IMC 2012 solutions. Longer versions with investigations: Solutions and investigations (PDF).