Traffic Lights

Finding the Secret Number

When we first devised the Traffic Lights game, we played it with a High School class at Kulkarriya Community school, situated on the banks of the Fitzroy River deep in the heart of Western Australia. We were looking for a way to make the spoken use of large numbers have a purpose and found that, after initial difficulties had been cleared up, the students were fluent in their ability to write down and say a 4-digit number as they guessed what the secret number might be. Soon we were able to move on to 5-digit and 6-digit numbers which everyone was reading and saying correctly. But we also found that having this goal for the game meant that two rules for the secret number had to be followed:

• Rule 1: The first digit must not be a 0, because in the decimal system, numbers do not have a leading zero.
• Rule 2: No digit must be repeated in the secret number.

Allowing repeated digits substantially increases the difficulty of finding the secret number, particularly when searching for a 6-digit number. It wasn't our goal to make the puzzle difficult as there was plenty of challenge initially in being able to say the number using place value correctly. Once we had fixed the rules, the game soon became a favourite with the class and was often used as a quick warm-up to a maths lesson. We also found that the game had another important value.

Developing logical thinking

In order to find the secret number in 6 moves or less, you need to think logically about the meaning of the information that the traffic lights provide. If you find that your child is making apparently random guesses then questions such as the following will help them be more logical in their approach:

"This digit in the thousands position is one of the correct digits. Which other positions could you try for it?"
"Which digits have you not tried yet? It would be good to see if you could eliminate some of them."

In the Classroom

The Traffic Lights program supports the Year 3 and Year 4 statements for number recognition in the Australian Curriculum: Mathematics. In the lesson plan given below, you will see how the app can be used for a Mental Routine and as a Game to develop number sense.