WIBU to just teach DS how to do 'normal' division and multiplication?

[morninglive]

He is 7 and homeschooling via zoom. Teacher did some work where the kids had to use a model bar to multiply lengths of metres cm and mm, to make the larger length. as in - the house has storeys 4m 30cm and has 5 storeys. how tall is the house? As if multiplying and division in lengths isn't hard enough!

Instead of a straightforward multiplication in columns she did 4x5=20. 3x5-15. add them together and then some other shit. I just didnt understand it. Then a similar thing with division. Just gave the lengths of rope and said x 5 will give us the length of the uncut rope. Another example ...we have 350, halve it to get the two lengths of ribbon. But no explanation of how to halve that number. I think DS is very average so he couldn't even get started.

AIBU to say just teach in a secondary level way, but keep the numbers very simple. I am not talking long division here, or fractions of numbers (we also had those along with the metric shit) Yesterday was horrendous

the house has storeys 4m 30cm and has 5 storeys. how tall is the house? As if multiplying and division in lengths isn't hard enough

There's some interesting maths in there and some good maths skills.

1. Converting to metres
2. Knowing how to multiply together

Knowing that 1 m = 100 cm
Then adding together to make the height of one storey = 430 cm

Then knowing how to multiply 430 x 5

Different ways of doing that - 400 x 5 plus 30 x 5 = 2150 cm

And convert to metres

Or you could do 4m x 5 = 20m
30 cm x 5 = 150 cm - and then convert that to 1.5m

Or 4.3 x 5 and do either the grid method or more formal multiplication.

The tricky bit for some is the conversion between metres and cm. Some children might answer as 170 m or 170 cm (adding the 20 and 150)

Then there's the converting back eg. from 2150 cm to 21.5 m

Some could like the decimal route.

It's a good 'differentiation' task - with no ideal route - a lot of it depends on the understanding of the task for the pupil.

Tons of Lego so I'll look at those

You can put Lego people into ratios. That's fun.

I need 3: 2 ratio

@rosy71

"Can anyone then explain how to do 350x5 using the correct method?

And 250 divided by 6 as an example of division?"

Were these really questions given to 7 year olds?

I can't imagine they were given 250/6 at age 7, the object will have been to learn to use their knowledge of multiplication, I doubt they will have been taught how to deal with remainders of that magnitude!

As an aside, I was a maths teacher, up to A level but when I was doing the odd bit of supply while the children were small I worked in Primary schools! I learned more about how things work than I'd ever done before, I am a baby boomer so we were taught the algorithms to get the right answer without questioning what we were doing. Do any other seriously oldies think they could explain subtraction with 'borrowing'? Something like 3005 - 1976, not just the answer but the why??

Writing about my supply teaching in Primary schools reminded me of the time we were doing a 'project' about life in World War 2. I taught them £ s d, yd ft in, st lb oz and lots of other pre decimal maths. They were most impressed that their grand-parents had done this hard maths at school, no simply dealing with mutliples of 10, they had to deal withand know lots of other conversions. One boy said he had a new respect for his grand-parents, 'I thought they were dead thick'!

My problem is I can’t explain any of it! To use chomalungma’s 25 x 8 example. If it was me working that out on my own.

Firstly I just know it is 200 as I know my multiples of 25 times (easy to work out and use frequently at work and at home as I think of 25 as a quarter of 100).

Assuming I didn’t know I would then know that 25 x4 is 100 so it just follows that 25 x8 is 200.

Other variations of that, say 24 x8 I would round up the 24 to 25, get that 25x8 is 200 then get rid of my extra eight 1s so the answer is 192.

So I basically round up or down to the nearest easy number then work out the precise number at the end. I would always double check tricky sums with a calculator to be sure if the answer actually mattered.

Can anyone explain what method I am using and if it is an appropriate method for primary? And am I estimating but in a different way? My year 3 child seems to be taught both partitioning and some weird way of estimating which is not my way!

OP, there are some maths books for parents which might be helpful and explain some of the methods. I have an Usborne one although I confess we are both still confused!

Thankfully my year 5 child has been taught the ‘old method’ this year by school.

This is a really useful guide to different steps in division

sandhills.oxon.sch.uk/wp-content/uploads/2019/12/Division.pdf

A lot of understanding division problems comes down to visualising the problem and what's being asked.

250 / 6 . Is it how many groups of 6 or divide 250 into 6 groups?
I love drawing out the problem - and seeing the links.
e.g 1 bus holds 6 people, so 10 buses hold 60 people.
This carries on for much later concepts

e.g. £1 = $1.60
So what would £150 buy?

I've attached some diagrams to show some examples. You wouldn't want to draw 40 buses though.

You can tell what generation I'm from when I say I just visualise the written out sum for 250 divided by 6 and go from there..... 6s into 25 go 4, carry 1 (which attaches to the 0); then 6s into 10 go 1, carry 4 (which attaches to a newly added .0) which leaves either .6 recurring, or more helpfully 4/6 which = 2/3.
So 41⅔

@modgepodge No, they are not recorded, just Zoomed. White Rose looks good.

@Andbearsohmy Yes, fecking power maths.

@Surlyburd Yes, it looks like partitioning, which I never had a clue about, although when I multiply 8x9 in my head (never got to grips with learning times tables) I do 8x10=80-8=72. which I find is quite easy, so I am partitioning!

@chomalungma As you say it was quite complex (I didn't say we also had to add on a roof). I laboured through it (converted all to cm) and we got to the end, but had a half cm left, which clearly had to be converted to mm. Thats when I gave up trying to explain to DS.

@hansgrueber Yes, sadly they were. we converted to cm to do the sum (calculation!) and had a half left over. So it had to be reconverted back to M and cm and then mm. That was my moment of exasperation. When DS does substraction he does the borrowing from the tens and hundreds and nicely converts the other numbers appropriately. I was very impressed.

@TooStressyTooMessy I think I work things out in a similar way. I failed miserably in maths at school, but ended up working in an invoice department so had to use many of those methods. My party trick is halving long numbers in my head in a few seconds.

English Grammer and we are doing present perfect tense lol. but thats a whole different story.

@chomalungma As you say it was quite complex (I didn't say we also had to add on a roof). I laboured through it (converted all to cm) and we got to the end, but had a half cm left, which clearly had to be converted to mm. Thats when I gave up trying to explain to DS

That is starting to get complicated!!

Roofs are nice though. And potential for a bit of Pythagoras....

@chomalungma That was the bar model I couldn't get. The principle is fine, but how do you know how many people to sit in each bus without formal division of the number. The bar model was left blank in some calculations?

they only wanted the height, thank god! @chomalungma

[quote morninglive]@chomalungma That was the bar model I couldn't get. The principle is fine, but how do you know how many people to sit in each bus without formal division of the number. The bar model was left blank in some calculations?[/quote]
I suppose it depends how you define 'formal'.

It's more the opposite.

You know that you have 6 buses. So you want to split it out fairly. Like with money.

So it could be 1 person in Bus 1, 1 in Bus 2 etc to Bus 6
Then repeat.

But that takes a LONG time

Is there a quicker way?

10 in a bus
Or 20 in a bus

(If you are very good, you might know it's 40 in a bus)

Always look at what's left over - so you have 250 people, then you have 60 in already and keep building up.

It's either 'chunking' or adding groups.

It's like handing out sweets / chocolates etc to a fixed group of people.

Can you find a quicker way using your multiplication knowledge?

Or can you find a quicker way of making groups of 6?

MiddlesexGirl yes! When I visualise it I see the numbers / digits written down. I find it really hard to visualise numbers as dots or Lego or quantities as they are asked to now. I do get that it makes sense for understanding but my brain doesn’t work that way.

I feel your pain OP, sounds as if we do it similarly yes.

That division link is brilliant chomalungma thank you.

@chomalungma

Ah, yes haha!

I think whatever method works for him is probably more important than the rest. He may need to know the school method so he can follow. Have a look on bbc bitesize maths, they tend to follow the curriculum and can give you an idea. In an ideal world, the method would be whatever is most intuitive to him, but I'm free to think that way coz we homeschool and this less a philosophical debate than a what gets him through debate. We use Maths Factor, think they have a free trial and it's meant as a supplement to the curriculum. Videos and exercises, little steps, lots of repetition to ensure it's understood.

Thanks for the link choma!

@chomalungma when you put legomen into a 3:2 ratio do you put, say 6 legomen on one side znd four on the other, or do you have 6 whole lego men on one side and 6 legomen missing one third of their body (say, the legs) on the other?

[quote Babyiskickingmyribs]@chomalungma when you put legomen into a 3:2 ratio do you put, say 6 legomen on one side znd four on the other, or do you have 6 whole lego men on one side and 6 legomen missing one third of their body (say, the legs) on the other?[/quote]
That would be just mean.

Ideally you need lots of them.

Then it's 3 on one side, 2 on the other.

And keep carrying on.

Lots of talk about fractions, ratio and proportion.

If you take half the legomen’s legs off you can immediately demonstrate a 3:2:1 ratio though 😂 the :1 group is just all the detached legs

It all gets a bit complicated if some of the legomen have detachable hair though

@Babyiskickingmyribs

If you take half the legomen’s legs off you can immediately demonstrate a 3:2:1 ratio though 😂 the :1 group is just all the detached legs

Well you can imagine some of the conversations in primary school about what to do with the remainder when you are trying to put them into groups!

You have 1 person left - why not half them! It would be messy but it would be correct.

More interesting with chocolate. How do you share the last 2 bars of chocolate between 3 people?

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