I had wondered if talks about the boys’ study of the story of maths would be difficult to put together. When Eldest chose to research Times Tables, I wondered how easy it would be to come up with demos.
In the event, he had plenty to say and show. I encouraged Eldest to try and find patterns of his own in the multiplication tables by colouring them in on number squares.
We explored this Japanese method of multiplying numbers by drawing lines and counting the intersections. Eldest decided not to include this in his final presentation, but I thought it was great, and much easier than drawing endless bags of sweets (my usual multiplication illustration).
He did find out about the joys of the eleven times table. He also discovered that
ab + b(10-a) = 10b
He didn’t put it like that, but I found his explanation complicated! If you set out the times tables from one to nine in a grid. Take any sum you want (except the fives), then find the sum in the same column that is equidistant from the edge (which is why you can’t use the fives). Add the answers together and you will have a number in the ten times table.
By way of example:
3×4 is the third from the top in column three.
7×4 is the third from the bottom in column three.
40 is four tens.
It’s not going to change the face of modern mathematics, but Eldest was having fun with numbers and enjoying making his own discoveries. Good enough.
Middly’s talk was on 3d shapes. He made some, using nets I gave him:
He drew a plan, with a key, showing his designs.
He told us the names of many solids. He even introduced us to the concept of anti prisms (thanks to Wikipedia).
Finally he drew on our white board:
cm³ means cm cubed
Because, as he put it: ‘it’s true, but it doesn’t mean anything if you say it out loud.’
I am pretty happy with our first maths presentations. The boys have chosen to research abacuses and sand timers next!