National Maths Day 2008 Damian Howison MacKillop College, Swan Hill, Victoria Damian's wife Catherine, who also teaches at the school, but not in mathematics, is renown among the staff for her culinary skills. Generously, she spent the evening before National Maths Day baking Chocolate Chip Digit Cookies for afternoon tea. See below how they were used to focus the flagging concentration of the maths staff in the last quarter of an intense PD day.

May 23rd was a pupil free day and maths staff organised a workshop to support their efforts to integrate a task centre and Maths300 into their curriculum. (See Damian's previous story.) It was also National Mathematics Day so among the other hands-on materials were Chocolate Chip Digit Cookies.

Can you arrange the digits into a 'plus' sign so that the sum of the digits in the vertical arm is equal to the sum of the digits in the horizontal arm?

Well done. Now how do you convince me that the sums are the same?

Easy, 9 pairs with 1, 8 with 2, 7 with 3 and 6 with 4. That's 20 in each arm and the 5 is shared. Great, but a mathematician asks: Can I check this another way? This question generates informal, incidental teaching moments which: validate student 'ways of knowing' reinforce that there is more than one way to look at any maths problem confirm that our curriculum is about learning to work like a mathematician

And what happens if there is a different number in the middle, say 9? If it does work with 9 in the middle, are there other solutions? If so: How many solutions are there? How do we know when we have found them all? For more information, investigate Task 35, Crosses.

Then celebrate your solutions like this.