Marbles
identify and continue a repeating number pattern (1..3..5..7)
This problem gives a good opportunity to reinforce counting in twos, using different starting points (eg 1..3..5 or 4..6..8).
This problem mixes several things together. First the students have to realise that Katie has a sequence of 1, 2, 2, … and that that adds up to 1, 3, 5, 7, … on each successive day. They then have to work out when this sequence gets to 11. The final step is to convert that number of days into a day of the week.
All these steps by themselves are not too hard. The difficult thing is to find a way to record all the steps and then put them all together.
Problem
Katie was given a marble on Tuesday. Then she was given two marbles every day for a long time. When did she get her 11th marble?
Teaching sequence
- Introduce the problem by "acting" the start of the problem using a student.
- Brainstorm for ways to solve the problem (use equipment -counters or bottletops, draw).
- As the students work on the problem in pairs ask questions about the patterns they are using?
How do you know how many marbles to add each day?
Can you count the counters you have put out?(note if they count in twos)
How could you convince the others in the class that you are correct? - Share solutions to the problem.
Extension to the problem
When did Katie get her 30th marble?
Solution
One way to do this is to put out 11 counters and have some cubes ready. We will use the cubes to count the days. Count out 1 for the first day and record a single cube. Then count out two and record by adding a second cube. Then count out another two counters and record a third block. We show the count in the diagram.
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Here it can clearly be seen that it takes 6 days for Katie to get 11 marbles.
This could perhaps be done more easily by:
1 + 2 + 2 + 2 + 2 + 2
Tu We Th Fr Sa Su
Solution to the extension:
How can Katie get 30 marbles? She started with one. If she gets two more every day she will ever only have odd numbers of marbles. Since 30 is even she will never get 30 marbles. (She will get 29 and 31 but never exactly 30.)
| Attachment | Size |
|---|---|
| Marbles.pdf | 40.58 KB |
| MarblesMaori.pdf | 45.16 KB |
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