Lesson 3.1 FL Go Math 4th Grade
Math
Hi, boys and girls. Welcome back. For another teacher tube lesson, long time no see. today I'm gonna be starting on chapter three. We're gonna be doing 3.1 in your small math book, the math practice book. I'm going to go over a few of the problems and show you the methods that I used to solve the problems. And we're going to start with number three. Here we go. Number three says. 30 times 52. Okay? And the way that I'm going to solve this problem is I'm going to say 30 times 52 is the same thing as 30 times 50 plus two. Because 50 plus two would give me 52, but if I break it up like this, it kind of helps me to solve it a little easier. So first I'm going to do 30 times 50. Now there's two ways you can multiply 30 times 50. But you could either multiply like this, do the double dip digit multiplication if you're comfortable with that, or you can do it the way I've taught you in class and just say three times 5, which is 15, and then there's one, two, zeros involved in the problem, so there should be two zeros in our answer. Gives us 1500. 1500. Now we just did the first step. Now the second step is to multiply 30 times two. Three times two is 6. There's one zero. So we have 60. Now, with this method, because this because we use addition here, we are going to take the two answers that we got and we're going to add them together. So 1500 plus 60 gives us 1000 560. And this method boys and girls is called. Mental math. We call that mental math. So anytime you take one of the one of the parts of the problem and you break it up into an addition problem, how we took 52 and broke it up as 50 plus two, that is using mental math. I'm going to do another one. And this time we are going to look at number 6. Number 6 in your small MacBook. Okay? Number 6 says ten times 90. For this problem, I'm going to use place value. And the place value method basically says that ten times 90 is the same thing as ten times 9 tens. And the way that we do this is we kind of just write the place value and word form so that it helps us to kind of visualize the problem a little smaller. So now we know ten times 9 is 90. But it's not just 90 because we can't forget the place value. It's 9 ten, 90 tens. And we can't leave the answer like this. We have to convert it now into standard form. So 90 tens would be. I hope you know. 900. And this goes back to the place value and renaming numbers when we talked about in chapter one. And for those of you in my class, you remember what the way we did the number line on the floor and I told you if a 9 in a zero or both in the tens place, somebody's got to get out. And the only place that they can go is up. So we move the 9 to the hundredths place and the zero stays in the tens place. And we get to 900. And that is using place value. The last method we talked about today was associative property. And I'm going to show you a problem using associated property. Let's see. Let's look at number four. Number four, okay? 60 times 20. Now the associative property looks a little like mental math, but instead of breaking the problem into something that you can add together or breaking the problem down into something that you can multiply together. So we are going to look for what times what can give me 20. Okay, I'm going to use. Ten times two. Because ten and two are easy numbers to multiply by and ten times two will give me 20. So now that I have my problem like this, 60 times 20 is the same thing as 60 times ten times two. Okay? So the way that I'm going to rewrite this problem. Is like this. Now I'm going to just multiply. 60 times ten. Gives me 600. Now I just multiply this part right here. 60 times ten. And the only thing that's left is times two. 600 times two. 1000 200. And this again is called associate of property. Now with these methods, I really want you to be able to understand how to use each method and how to solve emulsification problem using each of the methods, but whichever method you are more comfortable working with is what I want you to use more frequently. However, I would like you to try to exercise some practice in all of the methods that way you're comfortable with all of them. I'm gonna do a few more examples that these won't be on your book. Okay? Okay. 20 times 40. And for this, I'm going to use place value. So with place value, I'm going to do 20 times 40 is the same thing as 20 times four, tens. 20 times four, well, two times four is 8. But I have a zero, so it's 80, but it's not just 80. It's 80 tens. And then when I convert 80 tens into standard form. I guess, 800. That's using place value. I'm going to do one more using place value and then we're going to move on. Ten times 70. Ten times 70 is the same thing as ten times 7 tens. Ten times 7 is 70, but it's not just 70. It's 70 tens. And 70 tens written in standard form. The 700. This boys and girls is using the place value method. When you have a number, that's. Like 40 or 50, 60, even if you're in the hundreds. As long as it's an even number, it's easy to use place value to solve the problem. Okay? The next method that I'm going to show you some more practice in is associated property. We're going to use 20 times 40 again. Okay? So with associative property, we take one of the numbers and we find a multiplication problem to replace with that. So we need to think of what times what would equal 40. Well, the two numbers that I'm going to use are ten and four. Ten times four equals 40, and it's easy to multiply by ten and it's easy to multiply by four. So that's what I'm going to use. So 20 times 40 is the same thing as 20. Times four or four times ten. Okay? So I'm going to rewrite that down here. And then I just start multiplying. So I'm going to multiply 20 times four first. Okay? And when I multiply 20 times four, I get 80, and now I'm going to multiply 20 or I'm sorry, this right here, I'm going to multiply this entire answer, which is 80 by ten because that's what's left. So 80 times ten. 8 times one is 8. There's two zeros involved. 800. And that is associated with property. The last method I'm going to show you is mental math. And when we use mental math, we take one of the parts of the problem and we turned it into an addition problem. So for this, I'm going to do ten times 15. Ten times 15 is the same thing as ten times ten plus 5. Ten plus 5 is 15 and it's easy to multiply by ten and you're 5 facts should be easy as well. So when I do mental math, I'm going to multiply ten times ten. Right? And instead of taking this number and multiplying it now by 5, like you did an associate of property with mental math, we do ten times 5. And because we added here, we now have to take this addition sign and put it here. And add these two numbers together. And you should get one 50. So I hope this practice helped you, and I hope you understand the methods just a little better. Hopefully you can do some of the ones in your homework on your own. And if you need to go back over some of the methods, start the video over again or look through your notes that we took today. I know it's going to take some practice, but eventually you guys will get this. I hope this helps and I will see you tomorrow. If you watched my YouTube video and you took notes or you did some of the work with me, go ahead and put the code word fun. At the top of your paper. Right underneath 3.3 .1 right fun. FUN, I will see you tomorrow. Have a good day. Bye.