Let’s investigate 2

Ok mathematicians, let's investigate.

So yesterday you joined us for a number talk on different ways that we could think about to solve 15 nines, 15 x 9 and what we thought is we might come back today and investigate different ways of representing two of the three ideas and that would help us investigate how these strategies work so that you can then apply them.

So here's a representation of 15 nines. And now let's look at the first teams way of thinking. So they said, well 15 nines we know that we can partition the 15 so that we have 10 nines and 5 nines. Then they said we know something about 10 nines that we could actually use the communtative property to re-imagine that as 9 tens. And that would give us 90 and we also know 5 nines is 45. And then we could turn it back together. Rejoin our array. And find the total of 135.

And that's one way of thinking about it. But then another team said, well, we have a different strategy. Look, here's 15 nines and I can think of 15 nines as 15 tens. And this is helpful for me 'cause I can rename it in place value and then I just have to remove the 15 ones that I borrowed. So once I've got 150 I then need to remove the 15 ones and that leaves us with 135. And that was a second way of thinking through the problem.

So now we have two strategies that we've explored, but the third one we've left some mystery around. So mathematicians it's back to you now to see how you could use these ideas and representations to help you solve or to record your thinking around 16 twenty-fives.

Ok, over to you.