Number hide and seek

I've discovered a new and way of helping my children to understand something today - get them to teach each other! Specifically, asking my older daughter to explain something to my younger daughter, although I can see the method might have merits the other way round as well, if only to consolidate the understanding of a new topic, by having to articulate it.

Early this morning when I was still half asleep and my brain wasn't fully switched on, the 5 year old (who was the 4 year old for those of you who've read my earlier posts; she had her birthday yesterday) asked me why the number 520 didn't have a zero between the 5 and the 2 to show it was 5 hundred. We've all been in this situation - we're asked by our children to explain something we have understood for years and take for granted and we don't know quite how to start, especially when we've just woken up. So in a moment of genius I turned to the 7 year old and asked her to explain it. This method could be risky of course, as the older child could well have misunderstood the question, or not know the answer, or pretend to know and give the wrong answer, or end up totally confusing everybody with a complicated explanation that only she can understand. However, I was pleasantly surprised when she succinctly and clearly explained that the zero that shows that it is 5 hundred, is merely hiding behind the 2. Wow. We all got it and we were all happy.

When I thought about it I realised that this idea of a hide and seek zero is brilliant, as when children start to add up larger numbers, one of the ways that they are taught quite early on, is to break up the large numbers into easy chunks. (Consulting with the 7 year old, who is sitting next to me as an expert adviser as I type, she has just informed me that they call this "partitioning numbers"). This is something that as adults we often do as it's the common sense way of adding up large numbers in our heads, but I was certainly never explicitly taught it when I was in the infants. A number like 520 is actually 500 and 20 (ah - there's the hidden zero), so when we do the sum 520+334, we can think of it as 500+20+300+30+4. The great thing about addition though is that it makes no difference in which order we add the numbers together, so we can choose the way that seems easiest and most common sense to us. Probably something like 500+300, which gives us 800; then 20+30, which gives us 50. 800+50=850 and then add the 4, making 854.

Try asking your child to explain to you how they have learnt something in school, or ask them to play schools and "teach" you, or each other if you have more than one child. You might be surprised at how well they can explain something which you can then use as a basis for helping them with trickier homework problems later on.