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Original poster

Year 2 Maths......What the hell is a near double ????

52 replies

Nutcracker · 28/09/2004 20:05

I have just had Dd1 trying to explain it to me but i haven't the foggiest what she is on about.

She said say if i add 5 + 6 = 11, then i have to do 6 + 6 = 12. She said near doubles helps me remember that 11 is by 12.

I am confused and feeling very thick.

Justr came to type this and couldn't even remember what they were called so had to wake her up to ask her.

OP posts:
popsycal · 28/09/2004 20:06

ok...here we go.....

Lisa78 · 28/09/2004 20:08

Hang on Nutty - here is DS1 to the rescue!!!

6 + 6 = 12 is easier to remember than 6 + 5 = 11. So if you need to do 6 + 5, you don't, you do a near double - in this case 6 + 6 = 12 then minus 1!

Easy!

popsycal · 28/09/2004 20:08

basically lots of maths these days uses basics like doubling to work out trickier stuff

they learn doubles really early on and use them for loads of things: near doubles, multiplying by 4, 8 etc etc

All near doubles is for is of you are faced with 2 numbers that are nearly identical eg 6 and 7 and need to add them then you just work out what it would be for doubling one of them say 7+&-14 then think that 6+7 would be one less.

Using known facts to calculate unknown facts....
HTH

popsycal · 28/09/2004 20:09

lisa's ds explained it way easir than i did lol

Lisa78 · 28/09/2004 20:10

think our explanation is better than yours popsycal [sticking tongue out smiley]

Lisa78 · 28/09/2004 20:10

takes a bow

popsycal · 28/09/2004 20:11

i agree!
lol!
was trying to be teachery and explain WHY they are used as well....
the rationale behnd the methods

Lisa78 · 28/09/2004 20:18

honestly, teachers...

popsycal · 28/09/2004 20:19
Grin
Original poster
Nutcracker · 28/09/2004 20:32

Oh is that all. Phew feeling abit better now. Thanks loads Lisa (and your Ds ) and Pops.

Thinking about it that is sometimes how i get her to work things out so i have already been doing it, just didn't know it.

Now when everyone is in the playground asking what the hell they are I will be able to explain like i always knew

Thanks

OP posts:
Tessiebear · 28/09/2004 20:35

Ooooh this explains a lot about my Yr2 DS's recent weird way of working out his Maths ... ThanksX

JJ · 28/09/2004 20:39

In my day we had different rules for it -- commutative, associative, distributive and had to learn the words for it. Those did me NO GOOD WHATSOEVER. Ahhh, feels good to say that as in a previous life I did a lot of adding up type things.

Much better and more intuitive way to teach it.

SueW · 28/09/2004 21:43

This reply has been withdrawn

This has been withdrawn by MNHQ at OP's request.

JJ · 28/09/2004 21:46

Oh dear, my meaning was that the new ways are good. The old stuff was just confusing.

And thanks, Sue, for the math quiz! V good illustrations.

blossomhill · 28/09/2004 21:50

My ds hasn't mentioned these yet and he is in year 2. Personally I think they are confusing them with this method.

Shimmy21 · 28/09/2004 21:52

And in fact that's how we've all being doing mental arithmetic ourselves for ever. It's just that noone used to point it out so clearly in our day - the 99 +98 is a good example. If you were asked to do it in your head very few people actually do a mental 'downwards addition adding the units and carrying the tens etc

edam · 28/09/2004 21:54

Ooh, I've been doing this all my life! Does this mean I inadvertently started a trend? . It's the sort of thing I used to be marked down on back in the olden days...

edam · 28/09/2004 21:55

Damn, shimmy got in there as I was posting to point out everyone else does it too. Just when I was feeling clever... hey ho, back to the corner and the dunce cap...

blossomhill · 28/09/2004 22:03

Shimy21 - when you explain it like that I always have done that anyway!

Original poster
nutcracker · 28/09/2004 22:19

I have to admitt that i did think she was making it up at first as i really didn't have a clue.

When it seemed wuite complicated i did think it was making things more confusing but now i know what it is i can see how it would help.

OP posts:
sis · 28/09/2004 22:21

My dad is brilliant with mental arithmetic and uses loads of 'tricks' like this. He can work out vat on things really quickly by doing 10% plus half of that plus half of that again whereas I used to do it by doing 10%, doubling it and then trying to work out a quarter of 10% to take away... you can see why my dad'smethod is far more efficient!

marthamoo · 28/09/2004 22:45

Ds1 is learning a lot of these maths tricks to help with mental arithmetic. Makes my head hurt...always was crap at sums.

marthamoo · 28/09/2004 22:46

Calculators are very good...

KateandtheGirls · 28/09/2004 23:01

My degree is in maths. I think tricks like this are great to learn and understand.

My SIL and 9 year old niece were astounded a few weeks ago when I showed them the 9 times table trick of using your fingers. Did you all learn that at school too? Apparantly it wasn't taught in the US. SIL asked "but isn't that cheating?" I don't believe it is at all. So what if it means you don't have to learn the 9x table by heart? - all that is is memorization, not mathematical understanding.

marthamoo · 28/09/2004 23:04

9's were the only tables I could do - my dad taught me that thing with my fingers. Have passed it on to ds1!