Build it up

Can you find all the ways to get 15 at the top of this triangle of numbers? Many opportunities to work in different ways.

Problem

 
 

We start with any four numbers (not zero!):

 

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4 numbers in circles reading 4, 1, 2, 2 from left to right.



We then add them in pairs and place the total above them:

 

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3 circles placed on top of the previous 4 circles, with one circle stacked between each two circles on the bottom row. From left to right they read 5, 3, 4.



And we then add in pairs the new numbers we just got:

 

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Two more circles stacked on top of the previous 3 circles reading 8 and 7.



We do the same with those two numbers to get our final number:

 

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A final circle placed on top of the previous 2 circles, reading 15.



You need to find four starting numbers to place at the bottom so that the top number will be 15.

Try to find as many sets of four starting numbers as you can.

Think about good ways to do this. Maybe use a system!

What little change can you make to the rules to explore again?

What new ideas can you think of to make this different? Explore those!

You may like to take a look at the follow-on activity Build it up More.