Help me with DS(7)'s maths homework!

[LightShinesInTheDarkness]

These are the instructions:

Work with a partner:
You will need a set of shuffled 0-20 cards and a sheet of paper each
Take turns to take the top card and put it onto the table in front of you
Write as many subtraction sentences as you can using the number on the card.
The winner is the one who wins the most rounds

Coud you tell me exactly what you would do, please?

[Stigaloid]

Hmmm that does sound confusing - can you ask for further clarification or did the teacher explain it better in class?

[AMumInScotland]

How odd... what are 0-20 cards, and why does my house not have any.... how can you write 2subtraction sentences" with one number...? I'm baffled!

[JeffVadar]

What on earth is a subtraction sentence!? I thought you did sums with numbers.

These instructions make no sense to me at all. I would ask the teacher for a bit more guidance here.

[thumbwitch]

sounds nuts to me.
Doesn't sound like homework either - sounds like something they should be doing in class.

[stealthsquiggle]

Surely you need two numbers to do subtraction ?

What does DS say?

[singersgirl]

That sounds a bit odd. Couldn't you theoretically write an infinite number of subtraction sentences using any one number? eg 20-1, 20-2, 40-20, 41-20, 1,000,000-20, 0-20, -1-20?

I'm bored now so I'll stop. Are you supposed to choose 2 numbers? But even then you'll both get the same number of subtraction sentences.

[yappybluedog]

do you have to do 'subtraction sentences' with the 2 cards, ie, you have chosen the card and the other person has chosen the card, so you have 2 numbers, repeat by choosing another card?

that's how I would do it

[LightShinesInTheDarkness]

Thanks everyone - this is the homework DS brought home, and I queried it with the teacher. She has written me a note, saying that she explained it in class and also, (rather patronisingly I thought) that a 'number sentence' is a sum and DS is very familiar with this phrase.

My point to her is that these instructions are absolutely useless, especially for work which is to be done at home. Plus - DS is 7, so guess who is going to win each round - Mummy, or a 7-year old?!

[thumbwitch]

agree with her having a patronising tone - she might want to take a look at how badly well she is explaining her homework then if your DS is still struggling with it. (and you of course! ) Oh, and the rest of us....

[throckenholt]

um - 15 -- that is 20 take 5, 4 less than 19, 3 fewer than 18 - that sort of thing ?

[LightShinesInTheDarkness]

Thanks, thumb - I am not sure that explaining it in class is all that helpful when its me that has got to do it!

I can't believe I am the only person who queried this - did everyone else just make something up?!

[throckenholt]

I guess you can make it a game - DS says 15=17-2 you say ah but it is also 115-100 and 4030-4015

endless permutations of playing with numbers

[thumbwitch]

Do you know any of the other mums well enough to phone them and ask them how they did it? say your DS has forgotten what the teacher said and you need some clarification on what is expected.. they might confess they found it ridiculous too!

[thumbwitch]

I mean, even if you are only limited to using the numbers 0-20, there are still 20 different ways you could write a "subtraction sentence" with each number.

[DidEinsteinsMum]

0-20 cards are just bits of paper or card with the numbers 1 to 20 on.

I am guessing that it is something like
Indiv A get 4
4-0=4 20-4=19
4-1=3 19-4=18
4-2=2 18-4=17
4-3=1 17-4=16
4-4=0 16-4=15 ..etc

Indiv B gets 7
7-0
7-1
7-2
7-3
...etc

Is this just a thought exercise to get dcs to think about the multitude of ways to write sums quickly. Is there a time limit?

[throckenholt]

you could do a variety of games - eg the answer has to the number, the sum has to start with that number alone (eg 7- ? =), the sum has to start with the number (eg 76-?=, 700-?=), you have to take that number away (eg ?-7= )or it just has to have that number in it (eg 17-?=, 470-?=)

[thumbwitch]

But DEM, that is exactly my point - there are 20 sums available for every number, so where does the "competition" part come into it? It's formulaic! just an exercise in writing.
Unless the teacher meant something else.

[throckenholt]

you don't have to make it formulaic or stick rigidly to the rules the teacher suggested - surely it is just a a way of giving them practice in thinking about sums and playing with numbers. You can pitch it at whatever level they are comfortable with - and if you include older siblings too then they can have more complicated rules - eg multiples or negative numbers included.

[thumbwitch]

there you go lightshines - throckenholt gets it, you are saved!

[DidEinsteinsMum]

I would use a one min timer to give an alloted time to write the sums - its about mental arithmatic isn't it and how quickly you can process it. Not every child would identiy the 20 sums.

[throckenholt]

timer would depend on their confidence I think. I have a 7 year old DS who seems to have selective problems in not understanding numbers - somethings he gets easily others just stump him - and then suddenly it clicks. Adding a timer for him would just stress him and not make it fun. You will know your child best and can gauge when to introduce new rules to make it more challenging.

[LightShinesInTheDarkness]

Einsteins Mum - I see where you got your name from, you are Einstein!

What you worked out (and I didn't) was that where the instructions say :
'You will need a set of shuffled 0-20 cards and a sheet of paper each' they actually mean :
'Both people will need a set of 0-20 cards and a sheet of paper.'
I read it as ONE set of 0-20 cards between the two people, plus a sheet of paper each (presumably to write the answers on).

Thank you all - I think the fact that about a dozen (intelligent?!) mothers all had different ideas about what might be involved, just prove that the instructions were not clear enough.

I shall be down that school at 3 o'clock being a PITA mother.

[GrimmaTheNome]

Of course you read it as one set of cards, if you have a set each why would you need to take turns?

duh. Why do they have to use silly non-mathematical terms like 'subtraction sentences' ? If they don't want to use 'sums' as that can imply addition, then 'subtraction expressions' would be much better.

[DidEinsteinsMum]

thanks for the compliment!

I think ds is more einstein - i've just used to thinking outside the box

[titchy]

Well they're 7 year olds so year2, so wouldn't be expected to do any number sentecne with a 3 digit number, so how about child takes card 15 and writes down as many ways of making 15 using subtraction usuing the numbers 1 to 20. So they write 16-1, 17-2, 18-3, 19-4, 20-5, so get a score of 5. Mum gets the card with 18 on it and writes 19-1, 20-2, so gets a scor of 2. Child wins round 1.

Round 2, child gets card with 19 on it and writes 20-1, scores 1. Mum takes card with 20 on and can't write anything so scores 0. Child wins round 2.