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Maths teachers(and parents) please help No.2!

(6 Posts)
irvine101 Sat 27-Jun-15 08:09:49

My ds asked me, What is 3/0. I said 3/0=0.
But he said you cannot divide a number with 0.How can you?

Now I found out the answer is undefined, after googling etc., but how do you explain that to 6/7 years old? (He is yr2.)

Anyone help please?

AliMonkey Sat 27-Jun-15 08:18:00

We've had that conversation in this house and explained it like this:

If you are dividing a 3 by 0 then the question is really "0 times what equals 3". But
1*0 = 0
2*0 = 0
3*0 = 0
So every number times 0 is 0. So there isn't an answer to any question "0 times what equals y". Sometimes the answer to x / 0 is given as infinity, the logic being that however big you make the number, when dividing it by 0 you still don't get x. But you may not want to get onto explaining infinity to your DS ...

lougle Sat 27-Jun-15 08:21:22

I think it's something you just have to accept. The only way to describe it is that there is no answer that makes sense.

irvine101 Sat 27-Jun-15 08:24:00

Thank you AliMonkey! I will try that explanation. Infinity? No way I can explain that!!!

DeeWe Sat 27-Jun-15 09:53:09

Te way I did it with my dc when they were little was I showed them that if they say were dividing 21 by 7 you could do it as:
21-7=14
14-7=7
7-7 = 0
Took away 7 3 times therefore the answer is 7.

However:
3-0=3
3-0=3
3-0=3....
So how many times do you take 0 away from 3 before you get to 0... the answer they would give is that you can take 0 away all you like but it will never get to 0.

Infinity is something tricky to understand, but certainly possible at that age. We use it to effectively say goes on forever, which you can see in the above sum.

When ds was 4yo he got a fascination with infinity so we did a lot of things with infinity. Things like showing you can have different sizes of infinity (!) and definitions-one of his favourites was where parallel lines meet, which is quite neat when you think about it.

He had on his reception report "understands infinity". Apparently some of the children had been showing off how far they could count, and one said "I can count to infinity" to which he responded "you can't count to infinity, it's a concept not a number". Which was something we had discussed at fair length.

irvine101 Sat 27-Jun-15 17:49:34

Thank you lougle and Deewe! Wow, Your ds sounds really advanced,Deewe.

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