Teachers!! Please help me!

[HuwEdwards]

How do schools teach 'taking away'. DD in Yr3 and although I've found a way to teach adding up Tens and Units, how do you teach, 42-29, for example?

Counting back in 10s and units on a hundred square, then on a blank number line.Counting up from the smallest number to the biggest to find the difference.

In fact there's probably a whole host of people who aren't teachers, so please contribute if you can help

On a number line; count up from 29 to the nearest 10 which would be 30. So that is add 1. Then from 30 to 40 would be add 10. Then 40 to 42 would be add 2. So then do 1+10+2=13

ah thanks spud, is using a number square ok?

See Cece, she doesn't understand why, when the overall sum is a take-away, why you should be adding anything!

Ahh the emphasis is on finding the difference with that strategy. They need to be able to count up and down.
A hundred square is great at that age - everything must be as visual as possible.

If you call it counting on, or finding the difference, she might remember this bit from school.

For 42 - 29, another strategy we may teach is using close numbers and adjusting. 29 is close to 30, so:

42 - 30 = 12
12 + 1= 13
So 42 - 29 = 13

Another mental strategy she may know to subtract is partitioning - only partition the second number though.
So:

42 - 20 = 22
22 - 9 = 13

Hope this helps.

It is called finding the difference (so we use counting on or adding to find the differenc between the two numbers) and we use adding up because it is easier! LOL