IMC 2008 Q7
7. The square of a non-zero number is equal to 70% of the original number. What is the original number?
- A 700
- B 70
- C 7
- D 0.7
- E 0.07
Intermediate Mathematical Challenge 2008, Question 7. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: D 0.7
Let the original number be \(x\). Then \(x^2 = 0{\cdot}7x\), that is \(x(x - 0{\cdot}7) = 0\). So \(x = 0\) or \(x = 0{\cdot}7\), but as \(x\) is non-zero it is 0·7.
Solution © UK Mathematics Trust, from the IMC 2008 solutions.