11th December 2013 is the last date for 90 years that three consecutive numbers will line up.
Celebrate it in your school by using the date as a starting point to investigate consecutive numbers.

## 11 + 12 + 13 = 36

Which three consecutive numbers total 72?        (23, 24, 25)

What do you notice?

Do you spot any patterns when adding any three consecutive numbers? Try with smaller numbers.

Simplify:

1+2+3 = 6
2+3+4 = 9
3+4+5 = 12

Continue the pattern

What do you notice?  Do you spot any patterns when adding any three consecutive numbers?

(Sum is always multiple of 3, and it is 3 times the centre number)

Why does this happen?      Can you make up a general rule for this?

11/12/13 is also known as Noughts and Crosses Day as it shows three in a row (!), so make sure you celebrate it in your school.

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