To see if three horizontal rectangle numbers e.g. “12,13,14” – have the same result when you multiply the middle number by 2 and add the 1st and last number together.

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Diagram.1

Case.1:

To see if three horizontal rectangle numbers e.g. “12,13,14” – have the same result when you multiply the middle number by 2 and add the 1st and last number together.

Testing:

Conclusion:

This happens because the mean of the 1st and last number is equal to the middle number i.e.:        

Mean of 12 and 14 = 13

Middle number = 13

The next part of the scenario was to multiply the middle number by 2 and plus the 1st and last number together; this is the same result – it can be proven when we write as it’s shortest form i.e.:

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 +  = 2

2= 2

Formula:

Middle number multiplied by 2  = (First number) + (Last number)

Case.2:

To see if “Case.1” applies for horizontal and diagonal rectangles.

Testing:

 

Conclusion:

The original formula (Case.1) also works for Variable.2.

Case.3:

Investigate what happens when Mary draws a rectangle around five numbers.

Testing:

I first tried to see if the formula for Case.1 applied for Case.3:

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