# Lesson video

In progress...

Hello everyone and welcome to maths with Ms. Dobrowolski.

In today's lesson we'll be reviewing addition and subtraction strategies.

Looking at our lesson agenda, it looks like we have addition strategies up first, followed by subtraction strategies then we'll be ready for independent task and then the final quiz.

For this lesson you will need a pencil and notebook.

If you don't have these items, pause the video now and go get them.

So, first step we have addition strategies.

It looks like I have the equation 34 plus 29.

Now, what are some ways I could solve this? Should I partition the second number? Should I partition 29? Should I partition both numbers, the 34 and 29? Because I can see I can partition both numbers into 10s and ones.

Should I use the round and adjust strategy? After all I can see that 29 is only one away from 30, so maybe I can round and adjust.

Or maybe I could look for near doubles.

If I was to solve this, I would probably use the round and adjust strategy.

So I would round 29 to 30, and then make sure I subtract one.

So 34 plus 30, well I know three plus three is equal to six, so 34 plus 30 must be equal to 64, and then I'll subtract one because I know that I've gone over just one when I round it.

What I'd like for you to do is have a go and think, how would you solve these equations? What strategies would you use depending on what numbers you're adding? So for example, the strategy I use to add 27 plus 14 might be different from the one I use to add 23 plus 29.

And that's because in 23 plus 29, I can see that 29 is close to 30, so I would use the round and adjust strategy there, whereas for 27 plus 14, I can see that 14 can be partitioned into one 10 and four ones.

So I would partition the second number.

Pause the video now, I don't want you to solve them, I just want you to have go at thinking what strategy would make sense for you.

Pause the video and then resume when you're ready.

Great job everyone.

So, hopefully you've gone through all of these and you've thought about which strategy you would use depending on the numbers that you're adding.

And there's many different ways you can answer this.

Just because I added a certain way doesn't mean that that's the strategy that you would use.

So for example in 39 plus six, well I would probably just use the make 10 strategy there because I know nine plus one is equal to 10, so 39 plus one is equal to 40, 40 plus five is equal to 45.

And in 23 plus 29, maybe you partition both numbers.

But I saw that oh, 29 is close to 30 so I'll round and adjust.

I'll do 23 plus 30 and then subtract one.

Let's try that now with subtraction.

So I can see, I have the equation 53 minus 19.

Well, what strategy could I use here? Should I partition the second number? Should I partition both numbers? Or should I round and adjust? What would you do? For me, I think I would round and adjust, so I'd round 19 to 20 because 19 is only one away from 20.

So 53 minus 20 would be 33, and then 33 plus one would be equal to 32 and that's how I would solve it.

So what I would like for you to do now, is have a go.

How would you solve these equations? You don't need to find the answer now, that's not what we're doing.

All you need to do is say, oh I can see that in 52 minus 25 we can partition both numbers, so I'll partition each number into 10s and ones.

Or you might find that in 63 minus 19, you could either partition the 19 or you could round and adjust.

So you decide, how would you solve because there's many different ways you could solve the same equation.

Pause the video now, have a think and then resume when you're ready.

Super, so you've probably thought of a lot of different ways you could solve.

So for example, like I said for 63 minus 19, I would use the round and adjust strategy there because 19 is close to a multiple of 10, it's only one away from 20.

So I would round 19 to 20 and then add back one to adjust.

Now, for your independent task you're actually going to use the strategies you thought of to solve these equations, and use any strategy you think is best for any of them.

So for example, for 27 plus 14, you don't have to partition the second number the way I think I should do that.

You could partition both numbers or you could use a different strategy there depending on what you think is right.

When you're done, you can resume the video and we'll go over the answers.

So, pause now, complete your independent task and I'll see you when you're finished.