Colourful jerseys

Problem

In a class there are 20 students. They are wearing jerseys of 3 different colours – blue, green, and red. The class was lined up in a way that the pattern of jerseys was:

blue, blue, green, green, red, blue, blue, green, green, red...

What colour jersey is the last child wearing?
How many students are wearing a red jersey?

Teaching Sequence

1. Using students in your class form a repeating pattern using shoe colour (eg., white, brown, white, brown).
2. Without telling the students what pattern you are using ask the students to join the line if they think that they could be the 5^th member of the pattern.
3. Ask them to tell you why they have joined the line. (Remember that they may have a valid reason even if it is different to yours.)
4. Repeat the process to see if anyone else could become the 5^th member of the pattern.
5. Pose the problem to the class. Check that the students understand that they are finding out two things: the 20^th person and how many are wearing red jumpers
6. As the students work on the problem ask them to explain the strategy that they are using.
7. Share solutions.

Extension to the problem

Ask the students to make up repeating patterns using members of the class.

Solution

The students can do the problem mechanically by writing down a table as below.
To answer the questions in the problem, students need to write the numbers 1-20 and arrange the counters for jerseys in the given pattern.

On the other hand, the students might notice that the pattern repeats itself every five students. So the first, sixth, eleventh and so on students have blue jumpers. Using this idea all the questions can be answered.

The last child is wearing a red jersey because 20 = 5 + 5 + 5 + 5.
There are 4 red jerseys and they are worn by the students at 5, 10, 15 and 20.