Maths - adding/subtracting negative positive numbers

[annielouise]

Hi
I saw a wonderful explanation on how to add and subtract negative and positive numbers in one of the comments, I believe by someone home educating but I can't find it now, even with an advanced search. Does it ring a bell with anyone? If I'd realised it was the next topic that my son was going to do I'd have printed it off. The explanation included concepts like borrowing if I remember rightly. Wish I'd paid more attention now.

[ShrinkingViolet]

can't remember the thread, but I made a number line with both positive and negative numbers, then used the same "jumping frogs" they used when they started adding and taking away in the beginning.

[throckenholt]

this thread ?

[annielouise]

throckenholt - this is the one, it's the section by DyslexiaTeach - brilliant. Thanks so much. If I'd remember the rest of the thread - BIDMAS and BODMAS - I might have found it through advanced search. Thanks for locating it and thanks too to ShrinkingViolet, a number line is great but actually getting your head round some of the negatives and positives is hard, if not impossible, for me too.

[throckenholt]

I remembered reading it and that it had the word bodmas in it so I searched on that

Hope it helps.

[lilyfire]

There was a really good physical demonstration of negative numbers with holes in the ground in the channel 4 Dispatches, Kids Don't Count episode 2, which you can still watch on 4OD, if you have time.

[annielouise]

I completely forgot the word BODMAS and must admit I don't ever remember being taught that at school (I did O level maths). Will watch the 4 Dispatches programme if I can find it. Thanks again.

[piscesmoon]

If you can't find it. The DCs went outside and dug holes. The hole was the negative number and the pile of soil was the positive number. Therefore if you had -3 and wanted to add +5 you had to take 5 of the piles of soil and you filled in the 3 holes and had 2 piles left over, therefore -3 add 5 = 2.

[throckenholt]

sometimes it helps to think of the minus as a direction. Assume all positive numbers have an invisible + and head in a give direction (eg up, or to the right), then a negative number goes in the other direction.

Adding to the number (eg x + y) makes the number bigger in the positive direction, and taking away (eg x - y ) makes it smaller, ie moves in the other direction.

So a negative number will be down or to the left.

5 - 4 is the same as 5 + -4 - ie start at 5 and move 4 back (in the other direction). The - effectively changes the direction of travel.

If that confuses you - then feel free to ignore it - but it may just help.