April 2017
Problem of the Month

from the International Singapore Maths Competition
The Lock Number

There are 4 keys and 4 locks.
What is the maximum number of times you need to try the locks so as to match all 4 keys to their locks?

Explain.
 

Solution to the Problem:

The answer is The answer is six tries.

If you try 3 keys on the 1st lock, you will know that the 4th key is a match.
So, you only need a maximum of 3 tries.
Similarly, the 2nd lock needs a maximum of 2 tries and the 3rd lock needs only 1 try.
Thus, 3 + 2 + 1 = 6 tries are needed.

Correctly solved by:

1. Martin Round	Studley, Warwickshire, United Kingdom
2. James Alarie	Flint, Michigan
3. Mr. Paul Carignan's class	Naples, Maine
4. Vasilios Loutrianakis	Park Ridge,Illinois
5. Jonathan Spychalski	Park Ridge,Illinois
6. Amy Sorensen	Giddings High School, Giddings, Texas
7. Miko Zhang	Delta High School, Delta, Colorado

Send any comments or questions to: David Pleacher