0.6 x 2

1.4 x 7

8 x 5.4

0.7 x 14

Multiply a decimal number by a whole number

﻿Hi again, everyone. Welcome to the lesson. Today's lesson is to solve multiplication problems using known facts. Now, before we get started with the lesson, I have got a joke for you. How do you make a squirrel like you? You have to act a little nuts!! Come on, squirrel, nuts, eat nuts, no? Okay, right. Anyway, let's get on with the lesson then. So let's first have a look at our agenda in today's lesson. So first off, we're going to try and revise and think about using known facts and practise a little bit. Then we'll use that and apply it, how we can solve it using different currencies. Because today's lesson, we're going to use the context of some travel. And then we're going to think about converting pounds into other currencies and how that might work. And then lastly, we're going to do an independent task, to practise all that and bring it together. So make sure, you will need, you've got a pencil. Make sure you've got a ruler with you, and make sure you've got some paper with you so you can make any notes and solve, any problems let's go on with the warm up then, known facts. What we want to do is take facts that we know and use them to be able to help solve other problems and solve perhaps more complicated problems. So let me give you an example. If I know that five multiplied by eight equals 40 then I know other things. So I might be able to say using my knowledge of multiplication. I know that five multiplied by 80 will be 10 times greater. So the answer is always going to be 400. Okay? So we're using our known facts to be able to support us. So five times eight is equal 40. Then five times 80 is equal four hundreds. Likewise, I could also use that for division. The 400 divided by five is equal to 80. I could also think about. I know things greater. I can then think 10 times smaller. So this time 10 times smaller than five is 0.5. And I know that then my answer is going to be 10 times more as well. So 0.5 multiplied by 8 is equal to four, likewise, the other way around. Or I can think of making both parts 10 times greater. So my answer is then going to be a hundred times greater. So 50 multiplied by 80 is equal to 4,000, or I can then think both popping 10 times more with my answer is 100 times more. Okay. So lots of different ways that we can use our known facts. now over to you. So in this case, I've got, if I know seven multiplied by eight equals 56, then I know, and it's over to you. So I want it to pause the video. I've given you some that you might want to complete there, but also space to think of your own. If you can think of any more than the three spaces I've got, then go for it. I think of the many, if you can, and when you're ready play the video and we'll have a look. Okay. So what did we come up with? Well, seven multiplied by eight hundreds equals 5,600. But to be able to tell that from our known facts that we've got that, Oh, sorry. I think I've just missed out that last zero. Sorry about that. 0.7 multiplied by eight equals 5.6, and 500 divided by eight equals seven piece. We are using our known parts to help us solve the problems. I wonder which ones you came up with that brings us nicely into the day's lesson. So one thing that we can sometimes struggle with is when we're on our holidays, we have to use a different currency. And an example is one of our friends at Oak travel has been on holiday to Vietnam. Now Vietnam has got a different currency. They use the Vietnamese dong. Now the Vietnamese dong, for every one pound. There are 30,000. 30,000 in one pound. Okay. Lots of big amounts of money, lots of big denominations of money there. So we have to be able to get our heads around and to use your known fats can really help you to solve problems. So let's have a go and let's have a look at one. Now just help me a little bit by putting on known fact in the corner. Now, Vijaya wants to buy a Vietnamese lantern. And it costs approximately seven pounds. but saying it costs seven pounds. Isn't going to help when you're in Vietnam, she needs to know how much it costs in their currency. So, how much will that cost? How are you going to work it out? So pause the video and have a bit of a think. What you might do. You might have draw some things, you want to write some things down. How can you use your known facts to help you? Okay. When you're ready, play again. Okay. Over to me then the first thing I did when I did this is I think I need to be able to see this problem to be able to make sense of it. So the first thing I thought of is, well, I'm going to put out a layout, My seven pounds is going to cost. I know my conversion rate. There's going to be 30,000 dong in each one. So you can see the thousand. And that made me go straight into, I can use the bar model to help me here. However, I need to be able to solve this. I've got 30,000 multiplied by seven. Now I'm still a bit confused, but I do know my number fast. So I know that seven multiplied by three is equal to 21. So if I use that, I should be able to then say, well, okay, if seven multiplied by three, is equal to 21 then I know that seven multiplied by 30 thousands. Wow. So that's like 10,000 I'm multiplying by or making a great to them is equal to 210,000 Vietnamese dong. So I've used my known facts to support me, to help me to problem solve here. Let's have a look at another example then, but the different currency now Thomas from the United States is on holiday in Sweden now, even from the United States, I'm thinking in us dollars. So my conversion rate is from U S dollars to Swedish krona, which is the currency in Sweden. Now to help him to buy his snowboard. He's got $485 to spend. How many Krona is that going to be? Have a bit of a think. What could you do? What could you use to help you to be able to work this problem out? You may want to think of what do you know what's unknown? and maybe how can I represent this problem? Okay. And I give you a few seconds, so pause the video and have a think, and then we'll have a look at how you could have represent it. So my first thing I thought of is we'll probably use a bar model and it helped me to make sense of what I do. And I don't know, well, I know we've got $485 to spend. And I also know that Swedish krona is eight lots bigger. So that's going to be eight times bigger. So I've got my bar with eight parts to it, and I want to know how much it's going to be in total. So let's have a look at that representation over here. How am I going to then solve it? Well, lots of different crashes I could use and my bar model helps me see the problem, but it doesn't necessarily give me the strategy I'm going to use to be able to complete it. I know that I've got 485 and I need to make, and I multiply it by eight. But it's perhaps not as easy as that. So some possible strategies you could use to help you could be. Well, I can use my known facts, I have 485 multiplied by 10 is equal to 4,850, and I want it by eight. So if I can work out 485 multiplied by 2 and then subtract that. that's going to help me to solve the problem, perhaps easier than multiplying it by eight with long multiplication. that's one possible strategy. You might think. Well, what do I know about multiplying by eight, well actually? I know it's double, double and double again. So double multiply by two, then double again, multiply by four, double again, multiplied by eight. That could be another strategy you might want to use. If that's really one that you think is nice and efficient for you, another strategy you might want to use and thinking about well, 485 is kind of an awkward number. So perhaps an easier one to be able to work with is a 500 now 500 multiplied by eight is nice and easy as 4,000. Now the difference between 485 and 500 is 15. So if I work out the differences, subtract it, that's going to give me my answer. Well, I think that's a really nice, clever way of being really efficient. So that might be another strategy that you want to use in order to help you to solve it. Lots of different strategies we could use to help us to solve that it's about being as efficient as we possibly can. So now I'm going to give you a go, going back to our two different currencies. We've got the Vietnamese dong and I've given you the exchange rate on the Swedish krona. What I want to know is in my little bag of goodies, my box of objects, how much would these costs in their currencies, in the local currency? So you're going to have to work out. This is in pounds. This is in dollars. I want to know in that currency, how much would it cost? think about the different ways you could solve it? Think about the different strategies you might have and then try and work out, okay, off you, go pause the video now. And when you're ready, we'll come back and look at the answers. Right guys, how did we do? Let's have a look at some of those Answers. And then first off, think about our holiday to Vietnam. We know that the 30,000 in every pound, you might've gone first for three multiplied by 30,000. What would be a known fact there, perhaps three multiplied by three might've helped you slightly. Okay. We should have got that 12 pounds equals 360,000. 6 pounds.is equal to 180,000. Now, one day you did 12 pounds first because you use that to help you with six or vice versa. And actually if you've done three pounds, could you then work out six pounds? Cause it's double. And could you then work out 12 pounds because that's double again, right? So we can use some of these supporting facts to help us as well. Now four pounds for the spray is 120,000. And lastly 20 pounds, now what we could, we use here, perhaps, we could use our knowledge and pay 10 pounds. So one pounds then 10 pounds would be 300,000 and then double that again would be 600,000. Okay. Loads of different strategies. And I think the best way is just exploring, trying different things out and seeing how it feels. So we, I've got some of our answers there to . have a look at hopefully, work these out. Maybe you tried a couple of the strategies we looked at before. So converting to Swedish krona by eight, that double, double double, perhaps have a go at that and see if any of that Mo was useful to you. Okay. Let's start to think about this one then slightly more complicated now. So Ben is travelling to Japan and a taxi from the airport is going to cost him 12 pounds. Now in Japan, the currency is the yen and he has managed to get hold of a little exchange. So Here, you can see this is a conversion rate. this shows how much something would be in pounds and how much it would be in yen, converting it. So six pounds be equal to 900 yen, for example. So unfortunately it only goes to 10. So this is no use or is it, can we use this to help us to be able to solve how much 12 pounds would be in yen. Have a bit of a think. What would you do? What can you use to help you? Okay. So yes. So I've got 12 pounds. Maybe I can use something to help me. Now we know that n pounds is equal to 1,500 yen. We know that one pound is 150 and then we can add that too, or we can just go straight to two pound here and two pounds is equal to, 300 yen. So if I know that 10 and two is equal to 12 pounds, then I know that 1,500 + 300 is equal to 1,800 yen. Okay? So did you come up with that strategy? So as I said before, this lesson is all about being really flexible, really fluid and coming up with different ways to solve problems. Another problem for you then here, we've got some other currencies. We've got currency in India. We've got currency in Japan, in Mexico, the peso and we've got Brazil, the Real as well. how much in all the different currencies would you get if you had 15 pounds? So I've given you the exchange rate for one pound. How much would you get if you have 15 pounds? Okay. Pause the video. If you want to have a go at this, if you're not sure, then just play on a little bit, cause I'll give you a bit of a clue, some possible strategies that might help you. Okay. If you're looking for some strategies that may help you slightly, these might be some clues about how you might solve that problem. So have a look at that. If you're not sure have a go, maybe you could fix it or solve it more than one way. If you can have it, then pause a video when you're ready and you're finished and we'll go on and have a look at the answers. Okay. Hopefully we are done. So if I had 15 pounds, how much would I have in these different currencies? Well, some of the different strategies we put up there, we would have 1,500 rupees. We would have 2250 yen. We'd have 375 pesos. We would have 90 Brazilian Real. Now those are the different amounts. What I am interested in is you thinking about how you got there. So if you're watching this video with somebody else or you've got someone sat next to you or somewhere else, you can talk to compare their strategy to your strategy or talk through the way that you did it. Why was your way an efficient way? Why did that way make the most sense to you? Is there an easy way that you could have done it, reflecting on it now? Because what we really want to do is to be able to think about and reflect on how we've sold something. So that next time we can do it even faster, even more efficiently, great job guys. The reason I stress that then is because your task that you're going to do now, is going to be very similar to some of those examples we were just looking at. So think really carefully about the strategies you've used. Maybe try different strategies with different questions. So when you're ready, pause the video and go onto your worksheets and your tasks. And then when you've gone through and worked through them. We're going to have a look at some of those answers together. Okay? So let's have a look at some of the answers that we could have had then. So if I had 45 pounds in India, Japan, Mexico, or Brazil. Then I would have 4,500 rupees, 6,750 yen. 1,125 pesos or 270 reals, if I had 70 pounds. You'll see that I had 7,000 rupees, 10,500 yen, 1,750 pesos or 420 reals. Okay. If I had any 50 P, now this is an interesting one. If you know the currently rate for one pound, how are you going to work out? 50 P. Yep Nice and easy. Right? We just need to half it great. So hopefully we found 50 rupees, 75 yen, 12.5 or 1250 pesos or three reals. And lastly, we've got 150. What would the strategy used here? I wonder, Hey, lots of different strategies we could use. So perhaps say think about 150 and it's relationship there. So hopefully we got 15,000 rupees, 22,500 yen, 3,750 pesos or 900 reals. Okay. Thank you very much for your hard work today. Lots of numbers. What was great to see is I want to see lots of different approaches and thinking really carefully about how you're doing it compared to other people. And it's great to see other people's strategy cause they may have come up with something that you haven't thought about, or they may be able to show you a way that actually is better than the way you were doing, or you can show that to someone else. It was great to be able to share and discuss and explain strategies as much as possible. Now, if you would like to please do ask your parent on caretaker to share your work for you on your behalf. Okay. Thank you very much for your hard work guys, as always do please make sure that you can pull out your learning by going back and completing our end of lesson quiz. Thank you very much for all your hard work today. Hope you enjoyed the lesson. Have a great day guys. Bye bye.

If I know 7 x 5 = 35, what is 70 x 50?

If I know 8 x 7 = 56, what is 0.8 x 70?

In Mexico £1 is worth 25 Pesos. How many Pesos would you receive for £12?

In Brazil £1 is worth 6 Real. How much Real would you receive for £500?

In Japan £1 is worth 150 Yen. How much Yen would you receive for  £50?

Solve multiplication problems using known facts

In this lesson, we will solve multiplication problems in the context of currency.

Maths

Y6 Maths

Key Stage 2

Year 6

Solve multiplication problems using known and derived facts

Multiplication and division

Number

THEME

UNIT

Represent decimal numbers in a variety of ways

Place Value to 3 Decimal Places

Multiply and divide by 10, 100 and 1000 involving decimals

Multiply and divide by 10, 100 and 1000 with in context

Understand the terms 'common factor' and 'common multiple' as properties of a number

Identify properties of numbers

Use efficient strategies to multiply numbers, including decimals

Practise multiplication and division skills

Use formal written methods for short multiplication including multiplying decimals

Multiply by a two-digit number using long multiplication

Use formal written methods, including long multiplication, to solve a range of problems

Explore efficient mental strategies for division

Use the formal written method for short division

Use the formal written method of long division to solve appropriate calculations

Solve problems involving division with remainders (Part 1)

Solve problems involving division with remainders (Part 2)

Represent remainders in different ways depending on the context of the problem (Part 1)

Represent remainders in different ways depending on the context of the problem (Part 2)

Lesson overview:Solve multiplication problems using known and derived facts

Core Content

Multiplication and division: