IMC 2018 Q12
12. Someone has switched the numbers around on Harry’s calculator!
The numbers should be in the positions shown in the left-hand diagram, but have been switched to the positions in the right-hand diagram.
Which of the following calculations will not give the correct answer when Harry uses his calculator?
- A 79 × 97
- B 78 × 98
- C 147 × 369
- D 123 × 321
- E 159 × 951
Intermediate Mathematical Challenge 2018, Question 12. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: E 159 × 951
When the given calculations are performed on Harry's calculator, they will be equal to: A 97 × 79; B 98 × 78; C 369 × 147; D 321 × 123; E 357 × 753.
All of these, except E, are equal to the intended calculations.
Solution © UK Mathematics Trust, from the IMC 2018 solutions. Longer versions with investigations: Solutions and investigations (PDF).