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'Sending and Receiving Cards' printed from http://nrich.maths.org/
Why do this problem?
This activity represents a problem solving situation which may easily lead to a lot of reinforcement of number knowledge. It makes a good introduction to number investigations.
It would be useful before starting this activity to have done some work on Digital Roots
. Introduce the idea of digital roots, perhaps starting from what they notice about the answers to the 9 times table, before starting this challenge, as it adds a new dimension of things that can be studied and enjoyed in the exploration of this set of numbers.
Tell me how you are working these out.
How did you do your multiplying?
How did you do your adding?
A useful thing which may not have been experienced in number patterns before that works well in this investigation is to look at how the numbers that occur later on in the series can be made from the addition of previous numbers in the set. e.g. 110 = 20 + 90, all these three numbers being found in this number pattern from the sending of cards.
For the exceptionally mathematically able
You may like to read the article Opening Out
for more ideas of how to open out this activity for these pupils.
Use dolls/teddy bears etc. to represent the people sending cards and have something ready to represent the cards.