Maths Update: Adding/Subtracting 2-digit numbers

After revising partitioning, we recapped how to add 2-digit numbers mentally, i.e. partition into Tens and Units, add the Tens, add the Units, add both parts together. They also had the option of adding the Tens from one number to the other, then counting up the remaining Units, e.g.

28 + 43 =

20 + 40 = 60
8 + 3 = 11

60 + 11 =

60 + 10 = 70
0 + 1 = 1

70 + 1 = 71 so 28 + 43 = 71

OR

28 + 40 = 68
68 + 3 = 71 so 28 + 43 = 71

We concentrated on the first method first, to get them used to partitioning the numbers. Then we moved onto the second method as something more efficient.

After the mental practise, I introduced the column method to them as an efficient way of writing their working out down. It's the same principle, partitioning and adding each place value one at a time, but written in a compact way, e.g.

16 + 43 = 

   16
+ 43
   59

We started with numbers which didn't carry over into the next column, then once they were comfortable with the method I explained how to write the extra Tens underneath the Tens column - and to make sure they included them in their answer! e.g.

45 + 36 =

    45
 + 36
    81
    1

We also spoke about using a quick mental method to check their answers.

We did all the above through explanation and examples on the whiteboard first, then answering questions from a photocopied worksheet using the method we were focusing on at the time.

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Next, we recapped subtraction of 2-digit numbers via partitioning and counting down, e.g.

38 - 14 =

38 - 10 = 28
28 - 4 = 24 so 38 - 14 = 24

Where the numbers stayed within the Tens, then using numbers in the Unit column which meant counting down across Tens, e.g.

52 - 26 = 

52 - 20 = 32
32 - 6 = 26 so 52 - 26 = 26

After some practise doing this mentally, I then introduced the column method to them - but for numbers which wouldn't require carrying, e.g.

88 - 43 =

    88
  - 43
    45

I decided that was enough for now, so they could get used to the method, and we would look at carrying from the Tens column at a later point inshaAllah!

The above was all done, one method at a time on separate days, first on the whiteboard and then in the context of numbers by working through practise pages from one of the workbooks we have.

Finally, I gave them some word problems to work through so they could use these skills in the context of money. They had the choice to use either a mental or a written method, whichever they found easier.

More work with 10s

Just another self-reference post to show progress...

We did some more work on 2-digit numbers and adding/subtracting 10s. One of the girls found this a little more difficult than the other (the other was fine with an explanation then onto the worksheet) - I needed to model it for her a little more both with the multilink cubes, the abacus and writing colour coded examples on the whiteboard - so she could see visually that when adding/subtracting by 10 only the Tens are affected and the Units don't change at all. (Letts Make It Easy... Maths & English (Age 5-6) & Collins Easy Learning - Mental Maths (Ages 5-7))

We also did some work on the 10x table, by which I gave them the worksheets (Schofield&Sims - KS1 Problem Solving 2 & Letts Make It Easy... Maths & English (Age 5-6)) and the multilink cubes sorted into sticks of 10, read through the first question together as an example then left them to it... MashaAllah they were finished both sides within 10 minutes and without using the cubes at all! One of them laughed at me that I thought it would take them longer and they both laughed at me for taking the cubes out. 🙈 I tested them orally to check understanding and yes, they had either memorised or could quickly calculate their 10x table up to 10 x 10. 👌 Out of curiosity, I asked them what was 11 x 10? They weren't sure until I wrote it down for them to see, at which one of them got it straightaway. So I continued, then what was 20 x 10? That same twin understood it was 200 and 30 x 10 was 300 and so on; the other didn't get it - but that was just extra for my own curiosity. Not really something expected of them at this age! MashaAllah, I'm still super proud of them both. 💕

Word Problems with the PJ Masks!

My girls are all into PJ Masks at the moment... It comes on TV on TinyPop or you can find episodes pretty easily on YouTube (you can even find some dubbed in Arabic!). So I decided to utilise this by making up some simple word problems using the characters from the show.

Each sheet has 5 questions on it (a manageable amount for their age, I think). The first and second sheet have 1-step problems, the first focusing on addition and the second on subtraction. The third sheet has 2-step problems with a mixture of addition and subtraction.

We worked through them using cubes to physically represent the numbers. You could do it with a number line or whichever method you prefer though. We also wrote down each question as a number sentence (e.g. 5 + 2 =) before writing the answer, so they could get used to seeing how word problems translate into numerical problems. And we didn't do all the sheets in one go! We spread them out over a few days in between standard addition/subtraction practise just using numbers.

You can download the worksheets here. As always, feel free to edit as you wish - so you can change the numbers accordingly to make them more or less challenging. 😀